PEG-MGF: The Definitive Guide

What is PEG-MGF?

PEG-MGF is a lab-made peptide sold online as an injectable “research chemical” for muscle recovery and growth. It copies the last 24 amino acids of mechano growth factor (MGF), a form of insulin-like growth factor 1 (IGF-1) that muscle makes after it is stretched or damaged, and adds a small polyethylene glycol (PEG) chain to make it last longer. It has never been tested in people. [1], [2]

The name “MGF” causes most of the confusion around this compound, because it is used for three different things:

• The body's own MGF. The IGF-1 gene can be read in slightly different ways (splice variants). One version, called IGF-1Ec in people and IGF-1Eb in rodents, carries a short extra stretch of code that changes the tail end of the protein. Researchers found it in stretched rabbit muscle in 1996 and named it mechano growth factor because it appeared after mechanical loading. [3], [4], [5]
• The short MGF peptide. A synthetic copy of the last 24 amino acids of that tail (the “E peptide”), usually sold simply as “MGF”. Its human sequence is YQPPSTNKNTKSQRRKGSTFEERK, with a calculated weight of about 2,870 daltons (2.87 kDa). [6], [7]
• PEG-MGF. A modified version of that peptide. PEGylation means attaching a chain of polyethylene glycol, a water-loving polymer used in many medicines to slow their breakdown and clearance. [2]

The only published description of PEG-MGF's chemistry comes from a patent filed in 2005 by University College London and the University of Illinois. It replaces the arginine at position 23, next to the end, with histidine, uses the mirror-image D form of arginine at positions 14 and 15 so enzymes cannot cut there easily, caps the far end (an amide), and joins a PEG chain of about 1,900 daltons to the front through a small linker. Adding those parts gives a molecule of roughly 5 kDa by our calculation, much smaller than the 17,500 daltons some vendor pages state. No laboratory has published a test of what is inside vials sold as PEG-MGF. [1], [8]

Doserly

Six different things are called “MGF”

Evidence for one of these molecules does not carry over to another

The body’s own MGF (IGF-1Ec)

A version of the IGF-1 gene’s message that muscle makes after stretch or damage.

Evidence: Measured in human muscle samples after exercise; nobody was given anything.

Human data: Muscle-sample measurements only

Short MGF peptide

Synthetic copy of the last 24 amino acids of the tail (YQPPSTNKNTKSQRRKGSTFEERK).

Evidence: Cell and animal studies; failed an independent replication; did not switch on the IGF-1 receptor.

Human data: None

Stabilized MGF (“Goldspink MGF”)

The same peptide with Arg→His near the end, two D-arginines and an amide cap.

Evidence: Mouse heart studies by continuous pump at mg/kg a day; weakened healthy mouse hearts at some doses.

Human data: None

PEG-MGF This guide

The stabilized peptide plus a PEG chain of about 1.9 kDa (2005 patent).

Evidence: Patent experiments only: cell cultures, mouse strength, gerbil stroke, sheep heart and a plasma test tube.

Human data: None

Full-length MGF protein

A protein of about 12 kDa related to IGF-1Ec, found in products sold to athletes.

Evidence: Switched on the IGF-1 receptor in cell tests; characterized by anti-doping labs.

Human data: None

MGF gene transfer

MGF DNA in a plasmid injected into mouse muscle.

Evidence: About 20% heavier muscle and 25% larger fibres in 2 weeks; no new fibres.

Human data: None

No MGF molecule has been given to people in a published study.

PEG-MGF is not an approved medicine, and no approved product contains it. FDA placed it on its list of compounding ingredients that may pose significant safety risks in 2023; the nomination was later withdrawn, and an FDA advisory committee is scheduled to discuss it before the end of February 2027. It is banned in sport under the World Anti-Doping Agency's growth factor category. [9], [10], [11]

Typical PEG-MGF Protocols

The most common pattern in the reviewed sources is 200–400 mcg per injection, 2–3 times a week, for 4–6 weeks, followed by a break of about 4 weeks. Of 71 intermittent schedules on 55 PEG-MGF dosing pages, the single amounts most often stated were 200 mcg, and ranges most often ran from 200 to 400 mcg. None of these schedules has been tested in people. [12], [13], [14], [15], [16], [17]

Titration Changing the amount in steps

Most pages keep one amount for the whole course. The usual approach starts at 200 mcg twice a week and, on pages that step up at all, rises to 200–400 mcg two or three times a week from week 3. One widely copied plan instead injects every day, starting at 200 mcg and adding 100 mcg every two weeks to reach 500 mcg in weeks 7–8; that plan gives a much larger weekly total and is covered in Where do PEG-MGF protocols differ? [18], [19], [20], [21]

Timing

Sources split between injecting within about 30 minutes after training and injecting only on rest days. The rest-day habit goes back to bodybuilding forums from about 2010–2012, which used PEG-MGF on rest days and IGF-1 LR3 or plain MGF around training. [12], [22], [23]

Breaks and cycles

After a 4–6-week course, sources describe about 4 weeks off, or an off period at least as long as the course. The reason usually given is to avoid cells becoming less responsive, which has never been tested for PEG-MGF. [12], [21], [19], [18]

Read the units: mcg means micrograms; 1 mg equals 1,000 mcg, so a 2 mg vial holds 2,000 mcg. The amounts refer to PEG-MGF itself, per injection. When an amount is split between two muscles (“bilateral”), “200 mcg bilateral” can mean 200 mcg in total or 200 mcg on each side, so read the page closely. Several forum posts write “200 mg” or “400 mg” when they mean micrograms, a thousand-fold error. [24], [25]

Each row is a complete schedule from one source, and low, mid and high are alternatives, not steps to move through. These schedules come from dosing websites, not clinical trials: the page that supplies them says PEG-MGF has “zero human dose-response data”, and no study has given PEG-MGF to people. The cited references give the full details. [12], [26]

Cautions for every schedule above. None of these amounts has been tested in any person, and the in-body half-life that sets how often to inject has never been measured. FDA warns that PEG-MGF may provoke immune reactions and may contain impurities that are hard to detect, and it has found no human exposure data by any route. [2] In laboratory studies the human MGF tail peptide made prostate and breast cancer cells grow faster, so a current or past cancer is a specific reason for concern. [27], [28] It has not been studied in pregnancy, breastfeeding, anyone under 18, or alongside insulin, diabetes medicines or other growth-factor drugs. Products sold online are unregulated: seized “MGF” vials have contained modified versions of the peptide rather than the natural one. [29], [30] Check whether an amount is written in mcg or mg before drawing it; Doserly's reconstitution calculator shows each step. PEG-MGF is banned in sport at all times. [11] Read the full risks section

Where protocols differ: daily ladders, rest days, injection sites and breaks ↓

What is PEG-MGF commonly used for?

Most people who look into PEG-MGF want faster recovery from training, more muscle, or help with a tendon, joint or muscle injury. A 2026 medical review lists it among the IGF-1-related peptides most often found in online self-administration protocols, and personal accounts show it is nearly always added to programs that already include other peptides, growth-hormone drugs, testosterone or anabolic steroids. [36], [37], [38] In community education groups, it is most often discussed as part of a muscle-building stack or an injury “recovery stack”.

None of these uses has been tested in a human study of PEG-MGF. What follows separates what people hope for, what they report, and what animal and cell research actually measured, molecule by molecule.

Recovery and muscle soreness

This is the most common reason people give, and the most common thing they report. Accounts describe less soreness and training the same muscle again sooner: one person said they could train their chest hard on Monday night and again on Wednesday morning without soreness, and another that it “cut my muscle recovery time by half”. [37], [39]

No study has measured recovery or soreness with PEG-MGF or the short MGF peptide in people. Soreness depends heavily on training, sleep, food and expectation, and nearly every account involved other drugs. The community section looks at these accounts in detail.

Muscle size and strength

The hope is that PEG-MGF amplifies the signal muscle sends itself after hard training, so the same training builds more muscle. The body's own MGF signal does rise in human muscle after heavy or damaging exercise, as the human research section explains. That does not show that injecting a synthetic copy adds anything.

The only muscle data for the PEGylated molecule come from the 2005 patent: in normal mice, twice-weekly injections of 17 mcg into the shin muscle (tibialis anterior) raised its maximum force by more than 25% within a few weeks, and in mice with a form of muscular dystrophy force rose by up to about 35% after three weeks, compared with about 5% for IGF-1. The patent notes that the repeated injections may themselves have damaged the normal muscles. These results are patent data, not a peer-reviewed study, and they measured strength, not muscle size. [1]

The widely repeated claim of “20–25% muscle growth in two to three weeks” comes from a different experiment: MGF's DNA was injected into mouse muscle in a plasmid so the muscle made its own MGF. Two weeks later the injected muscle weighed about 20% more and its fibres were 25% larger on average, with no increase in fibre number. That was gene transfer, not a peptide injection, and not PEG-MGF. [40]

Tendon, ligament, joint and muscle injuries

Many people use PEG-MGF for injuries, often injecting near the injured area and combining it with BPC-157, TB-500 or other healing peptides. Accounts include wrists that stopped hurting after a year and a half of pain, injured knee tendons (“it healed them very effectively”, one person wrote), and an old arm injury that grew faster than ever before, alongside others who noticed no healing benefit. Physical therapy, other peptides and time were part of almost every story. [41], [42], [43], [44]

The injury research uses the short, non-PEGylated MGF peptide, almost entirely in animals and cells from a few research groups. A mouse study injected 5 mcg into a bruised calf muscle immediately and on days 1 and 2: it reduced scarring and inflammation markers but did not improve the regrowth of muscle fibres. Rat and rabbit studies of tendon, ligament, bone and cartilage injuries reported better healing. [45], [46], [47], [48], [49] The research library lists these studies.

Keeping muscle while losing weight

A newer reason is weight loss. People taking a glucagon-like peptide-1 (GLP-1) weight-loss medicine such as semaglutide, tirzepatide or the investigational drug retatrutide sometimes add PEG-MGF or plain MGF hoping to keep muscle as fat comes off. One person using retatrutide said the volume lost from their glutes came back after injecting plain MGF into them while weightlifting. [50], [51] In community education groups, several members describing PEG-MGF use were also taking retatrutide, and one educator warned that growth peptides are no substitute for enough protein and resistance training during rapid weight loss.

No study has tested MGF in any form during weight loss.

Heart, brain and other uses you may come across

Websites also mention heart protection, brain protection, nerve repair and anti-ageing. These claims trace back to animal studies:

• Brain. In the patent, gerbils given a single 25 mcg dose of PEG-MGF into a neck artery right after a brief stroke-like blockage kept far more of the nerve cells that normally die: about 83 per measured field on the injected side, against about 15 in untreated animals and 121 in animals without a blockage. The same research group published a gerbil study with a synthetic MGF tail peptide; its summary does not say whether that peptide was PEGylated. [1], [52]
• Heart. In sheep with an induced heart attack, the MGF tail peptide preserved heart function and left 35% less damaged heart muscle eight days later; the published paper's summary does not say whether it was PEGylated, although the patent reports a similar sheep experiment with PEG-MGF given into a heart artery. A stabilized, non-PEGylated version given by a slow pump helped mice after a heart attack. [53], [1], [54], [55]
• Nerves and ageing. Rat and mouse studies tested MGF peptides in models of Parkinson's disease and simulated weightlessness, and MGF gene transfer in a mouse model of amyotrophic lateral sclerosis (ALS). None involved people. [56], [57], [58]

None of these has been tested in people, and several used delivery routes, such as injection into an artery, that nobody uses at home.

Doserly

What PEG-MGF itself has been tested in

All six experiments come from one 2005 patent; patent data are not peer reviewed

Lab tests 3 experiments

Human plasma: Modified peptide still detectable at 24 hours, unmodified mostly gone by 30 minutes; the version without PEG also lasted 24 hours

Human muscle cells: Cultures from healthy, dystrophic and ALS muscle: more muscle precursor cells (about 38% to 58% in healthy limb muscle)

Rat brain slices: Tissue under chemical stress: fewer dying brain cells, with protection still seen at 48 hours

Animals 3 experiments

Mice: 17 mcg into the shin muscle twice a week: force up more than 25% (normal mice) and up to about 35% (dystrophic mice), vs about 5% with IGF-1

Gerbils: One 25 mcg dose into a neck artery after a 5-minute blockage: about 83 surviving neurons per field vs about 15 untreated (121 without blockage)

Sheep: Into a heart artery 15 minutes after an induced heart attack: more surviving heart muscle and better ejection fraction

People 0 studies

No studies. ClinicalTrials.gov checked 24 Sep 2026: 0

Animal doses cannot be converted to human doses.

Where do PEG-MGF protocols differ?

Sources disagree about how often to inject, when, where, for how long, and even whether the amount is weekly or daily. Here is what those differences mean.

Twice a week, or every day?

Most sources describe two or three injections a week. A second family of pages uses one injection every day, in an eight-week ladder: 200 mcg a day in weeks 1–2, 300 in weeks 3–4, 400 in weeks 5–6 and 500 in weeks 7–8, sometimes with 4 weeks off afterward. The same wording appears on several sites, so it is one plan copied many times, not independent agreement. [20], [59], [21], [60]

The difference is large. The table's mid schedule adds up to 600 mcg a week; the daily ladder reaches 3,500 mcg a week by its last two weeks, nearly six times as much. Community education groups show the same split: some courses give 200–400 mcg per week, others 100–200 mcg per day. In those groups, the members who described their own use injected between once and about four times a week, and none reported daily use.

Neither pattern rests on a measured half-life or a human study, and no one has compared them.

After training, or on rest days?

Many pages say to inject within about 30 minutes after training, when muscle repair is getting under way. Older forum protocols did the opposite: PEG-MGF only on rest days, with plain MGF or IGF-1 LR3 around training. [12], [22], [23] In community education groups, one explanation given for rest-day use is that a long-lasting version should not compete with the body's own post-workout signal.

Neither idea has been tested. The body's own MGF signal was measured as messenger RNA in muscle samples: it was raised 2.5 hours after heavy exercise in one study and peaked 24 hours after damaging exercise in another. There is no evidence that injected peptide competes with it or adds to it. [61], [62]

Subcutaneous, into the trained muscle, or near an injury?

Pages describe three habits: subcutaneous injection anywhere, injection into the muscle just trained (often split between both sides of the body), and injection close to an injury. The trained-muscle habit comes from older forum advice for plain MGF, which its discoverers described as a local repair signal made by the muscle itself. [12], [63], [64], [4]

PEGylation was added to help the peptide survive in blood, which undercuts the idea that it stays where it is injected, but no study has tracked where PEG-MGF goes after any injection. [1] Community education groups disagree on the same point: one course calls PEG-MGF systemic, another in the same group calls its action local. Injections into a muscle also hurt: one person described injecting the biceps as uncomfortable, and another said “the injection hurts like hell”, while a third felt nothing. [65]

How long is a course, and why the breaks?

Most pages describe 4–6 or 4–8 weeks of use, and some allow 8–12 weeks, followed by about 4 weeks off or a break as long as the course. [12], [13], [16], [63] The stated reason, preventing receptors from becoming less responsive, has not been tested for PEG-MGF, and no receptor for the MGF tail peptide has been identified (see how it might work).

Real practice is looser. In community education groups, one member ran PEG-MGF on and off for about a year and kept it going through the breaks from his other growth peptides, another ran 6 weeks on and 6 off, and injury users planned to stop once they recovered.

Plain MGF or PEG-MGF?

Plain, non-PEGylated MGF is usually described differently: often 50 mcg (ranges of 100–400 mcg on some pages), injected into the trained muscle straight after a workout. Some pages and forums treat the two as interchangeable; they are different molecules, and the doses do not transfer. [22], [23], [15]

Is there a consensus dose?

No. The recurring 200–400 mcg, two or three times a week, shows what circulates online, and many pages copy each other. None of the pages reviewed cites a human study of any PEG-MGF dose, and several say outright that none exists. Some cite studies of plain MGF released from PEG gel particles, which are not PEG-MGF (the PEG there is a carrier, not attached to the peptide). [66] Agreement between websites is not evidence that an amount is safe or effective. [12], [67], [68], [69]

These conventions are old. PEG-MGF protocols were already circulating on bodybuilding forums by the end of 2006 and in 2007, within months of the patent being published, with 100–200 mcg every third day or twice a week. [70], [71]

How do micrograms convert to syringe units?

Many people measure doses in “units” on an insulin syringe. A U-100 syringe holds 100 units per millilitre, so units measure volume, not an amount of PEG-MGF. How much each unit holds depends on how much liquid was added to the vial.

For example, a 2 mg (2,000 mcg) vial mixed with 1 mL of liquid gives 20 mcg per unit, so 200 mcg is 10 units. The same vial mixed with 2 mL gives 10 mcg per unit, so 200 mcg is 20 units. A number of units copied from someone else's protocol can be wrong by half or double. Doserly's reconstitution calculator works this out for any vial and shows each step. [12]

What happens when you stop PEG-MGF?

This has not been studied. No study has followed a person or an animal after a course of PEG-MGF ended, so there are no data on withdrawal or rebound effects, on whether any effect lasts, or on how long the peptide stays in the body. [26], [2]

• Personal accounts. One person who injected up to 300–400 mcg into the working muscle on most days said the effect faded after about two weeks, and that stopping brought “2–3 weeks of crappy workouts” before they felt back to normal. Nobody reported blood tests after stopping. [77]
• In community education groups, injury users planned to stop once they recovered, and no member described problems after stopping.

The breaks that protocols describe are a source convention, not a tested way to avoid harm or keep results.

Does PEG-MGF have to be injected?

In practice, yes. PEG-MGF is sold as a freeze-dried powder that is mixed with liquid and injected, usually subcutaneously (into the fatty layer under the skin) or intramuscularly (into a muscle). The patent lists many possible routes, including injection into a vein, but its own experiments injected into muscle, an artery or a heart artery, and never tested a pill, spray or skin product. [1], [12]

• Swallowed. There are no data on swallowing PEG-MGF: no study has measured whether any reaches the blood by mouth, and the patent's experiments did not test it.
• Nasal spray. One person described using PEG-MGF as a nasal spray and felt an immediate “cognitive benefit”, but found it too expensive for the amounts needed. No study has measured absorption through the nose. [78]
• Near an injury. Some people inject close to an injured tendon or muscle. The animal injury studies that did this used the short, non-PEGylated peptide, not PEG-MGF, and no study has compared injecting near an injury with injecting elsewhere. [45]

Bioavailability, the share of a dose that reaches the blood, has never been measured for PEG-MGF by any route.

What is the half-life of PEG-MGF?

It has never been measured, in people or in any animal. No study has tracked PEG-MGF in the blood of a living animal or person, so its half-life and how long it stays active are unknown. [26], [79]

Half-life is the time it takes for the level of something in the blood to fall by half. It is not the same as how long an effect lasts, or how long a drug test can detect it.

• What was actually measured. In the patent, the modified peptide and the unmodified MGF peptide were each added to human blood plasma in a test tube and kept at body temperature. Relatively little of the unmodified peptide could be detected after 30 minutes, while the modified version, which carried both the D-arginines and the PEG chain, was still detectable at 24 hours. In a second check in the same patent, the D-arginine version without PEG also stayed largely intact at 24 hours, so in the test tube the protection cannot be credited to the PEG chain. Either way, this is a test-tube stability check, not a half-life in a body. [1]
• Where the website numbers come from. Twenty of the dosing pages reviewed state a half-life, ranging from “4–6 hours” to “48–72 hours” and “several days”. None cites a measurement, and some say their figure is an estimate borrowed from other PEGylated drugs. The claim that plain MGF lasts only “5–7 minutes” has no primary source either. [12], [67], [68], [69]
• Why “days” is an assumption. The patent's PEG chain is small, about 1.9 kDa. Many PEGylated medicines carry much larger chains; a European Medicines Agency paper notes that in many cases the PEG is more than 40 kDa. How much a 1.9 kDa chain extends survival in the body has not been measured for PEG-MGF. [1], [80]
• The original MGF. The scientists who named MGF described it as having a shorter half-life than circulating IGF-1 when it is not bound to other proteins, without giving a number. [4]

Doserly

What the half-life numbers are based on

No half-life has been measured in any animal or person; the only data are a patent test tube

“48–72 hours” (PEG-MGF, on dosing websites)

An estimate; some pages say it is borrowed from other PEGylated drugs

No measurement

“5–7 minutes” (Plain MGF, on dosing websites)

Repeated online without a primary source

No measurement

Still detectable at 24 hours (PEG-MGF in human plasma, in a test tube)

Patent experiment: the modified peptide (PEG plus D-arginines) vs the unmodified peptide, little of which was left after 30 minutes; the D-arginine version without PEG also lasted 24 hours

Test tube only

Half-life in a living animal or person (PEG-MGF)

Never measured

Not studied

The patent’s PEG chain is about 1.9 kDa; many PEGylated medicines use chains larger than 40 kDa.

Once-or-twice-weekly dosing on websites is therefore a convention built on an assumed half-life, not on a measurement.

How should PEG-MGF be stored, and how long does it last?

No study has measured how long PEG-MGF keeps its strength, either as a powder or after mixing, so the answer is not established. [79] What exists is one line of general formulation text in the patent and conflicting advice on dosing websites.

• Powder, before mixing. The patent describes storing the peptide frozen or freeze-dried in sealed vials, with a sterile liquid such as water for injection added “immediately prior to use”. Dosing websites say to keep the powder in a freezer (−20 °C) or a fridge (2–8 °C), with one page claiming about 12 months refrigerated. None cites a stability test. [1], [12], [13]
• After mixing. Most pages say to mix it with bacteriostatic water and keep it in the fridge, but they disagree on how long it lasts: 7–10 days on some pages, 14–21 days, 2–3 weeks, or 28 days to 3–4 weeks on others. Some also say not to freeze the mixed liquid and to protect it from light. [81], [68], [15], [17], [16], [13], [12]

Community education groups argue about the mixing liquid. One side says PEG-MGF sticks to glass and breaks down in bacteriostatic water within days, so it should be mixed in dilute acetic acid; the other reports several courses in bacteriostatic water with no obvious problem. Neither side has tested potency, and people using acid describe a sting at the injection site. No stability data exist for either liquid.

This guide does not cover mixing or injection technique; the Academy note below covers practical handling.

What do we actually know about PEG-MGF in people?

No study has given PEG-MGF to people. Searches of ClinicalTrials.gov on September 24, 2026 found no registered study of PEG-MGF or PEGylated mechano growth factor; the six records that mention MGF only measured the body's own MGF, for example in muscle after training. PubMed lists no study of PEG-MGF itself, and FDA says it has not identified any human exposure data by any route. [26], [79], [2]

Has PEG-MGF been tested in human trials?

No, and neither has the short MGF peptide, the stabilized peptide or the full-length MGF protein. The patent's inventors wrote that they “envisaged” human doses of 0.2 to 10 mg, preferably about 0.5 mg, but that was a plan, never tested. Registry searches for PEG-MGF can also turn up trials of PEGylated growth hormone, a different medicine. [1], [26]

That leaves two kinds of indirect evidence: studies of the body's own MGF in human muscle, and cell and animal studies of various MGF molecules. Each answers a different question.

What do human studies of the body's own MGF show?

Several small studies took muscle samples (biopsies) before and after exercise and measured MGF's messenger RNA, the instructions a cell uses to make the protein. Nobody was given MGF in any of them.

Two points follow. Training already switches on the body's own MGF signal inside the muscle, although in one study it rose in young people but not in older people. And these studies measure a signal inside muscle cells; they say nothing about what an injected synthetic copy does. For years it was also unclear whether a free MGF peptide exists in the body at all: a 2010 review noted that none had ever been isolated from cells, tissues or body fluids, before the 2017 antibody study found one. [7], [84]

Where does the “20–25% growth” figure come from?

It comes from mouse gene transfer, described in muscle size and strength: MGF's DNA injected into a mouse muscle made that muscle about 20% heavier after two weeks, with fibres 25% larger and no increase in fibre number. It is not a PEG-MGF result and not a human result. [40]

Why can't the animal doses be used?

Because they come from different molecules, species and routes. The PEG-MGF experiments gave 17 mcg into a mouse's shin muscle or 25 mcg into a gerbil's neck artery; the stabilized-peptide heart studies gave 2.25 to 9 mg per kilogram of body weight a day for two weeks in mice. None of these can be converted into a human dose, and the milligram-per-kilogram amounts are in a completely different range from the microgram amounts on dosing websites. [1], [85]

How might PEG-MGF work?

Muscle can make several versions of IGF-1 from one gene. All of them release the same mature IGF-1, the growth signal that acts on the IGF-1 receptor in many tissues; they differ only in a tail piece (the E peptide) that is normally cut off. MGF's tail is unusual because a short insert in the gene shifts how the end is read, giving it a unique sequence. The idea behind MGF peptides is that this tail has its own job in repair, separate from IGF-1. [7], [86], [87]

Does it activate muscle stem cells?

That is the central claim, and the evidence conflicts. Muscle has its own stem cells (satellite cells) that multiply and fuse into fibres after damage.

• Supporting results. In the original group's cell studies, the MGF tail peptide made muscle cells multiply more and delayed them fusing into fibres. It increased the number of precursor cells in cultures from healthy people and people with muscle diseases, and extended the working life of stem cells from newborn and young adult donors but not from older adults. In mice, it improved the take of transplanted human muscle precursor cells. [88], [89], [5], [90]
• A failed replication. Scientists at two pharmaceutical companies tried to reproduce these effects. Native and stabilized MGF peptides at up to 500 ng/mL did not make mouse or human muscle cells multiply, did not delay their fusion, and had no effect on primary mouse muscle stem cells, while mature IGF-1 worked in every test. The authors concluded that the results “call in to question whether there is a physiological role for MGF”. [87]
• Species matters. Another group found that the human tail peptide stimulated human prostate cancer cells but not mouse muscle cells, while the mouse version stimulated mouse muscle cells, so a peptide can behave differently depending on whose cells it meets. [91]

The only test of PEG-MGF itself on these cells is in the patent. In muscle cell cultures from healthy people and from people with muscular dystrophy or ALS, it raised the share of muscle precursor cells (in healthy limb muscle, from about 38% to 58%) without changing how many fibres formed. That is patent data from cells in a dish, not a peer-reviewed study. [1]

Why do some MGF studies sound positive while others sound negative?

Mostly because they tested different molecules in different systems. Positive cell results used the short peptide, mostly from a few research groups; the replication tested both native and stabilized peptides and found nothing; injury and heart studies used the peptide in animals; the muscle-size figure used gene transfer; and receptor tests found that only the much larger full-length protein behaves like IGF-1. A result for one of these does not carry over to the others. [87], [92], [40]

Does it act through the IGF-1 receptor?

Probably not directly, although the evidence is mixed.

• In a receptor test, the human MGF tail peptide and its stabilized version did not activate the IGF-1 receptor at all. A full-length MGF protein, much larger than the short peptide, did, though it needed about nine times the concentration of IGF-1 to reach half its maximum effect (7.83 versus 0.86 nmol/L). [92]
• Early studies reported that the peptide worked even when the IGF-1 receptor was blocked, and suggested another receptor. No such receptor has been identified. [88], [82]
• A later study of the rodent tail peptides found they did not switch on the receptor themselves but increased the receptor's response to IGF-1, and their effects on muscle cells disappeared when the receptor was blocked. The authors concluded that the tail peptides “have little independent activity”. [93]

That matters for safety as well as benefit: PEG-MGF is sometimes described as a milder IGF-1, but its peptide does not behave like IGF-1 at the receptor, so neither IGF-1's effects nor its risks can simply be transferred.

What does the PEG chain do?

In the patent, PEGylation and the D-arginines were added so the peptide would survive longer in blood; the test-tube result is described in the half-life section. PEG chains can also change where a molecule goes in the body and how the immune system sees it, and none of that has been measured for PEG-MGF. Some community sources claim that PEGylation stops MGF acting locally, while others say it is the whole point; there are no data either way. [1], [2]

Does it create new muscle fibres?

That is a common claim, and it is not supported. Muscle grows by making existing fibres larger (hypertrophy), or in theory by adding new ones (hyperplasia). The MGF gene-transfer study found larger fibres with no increase in fibre number, and no study of any MGF peptide has shown new fibres forming. [40]

What are the risks and unanswered questions?

Is PEG-MGF safe?

Its safety in people is unknown, because no one has studied it in humans, and there is no animal toxicology program either. None of the PEG-MGF experiments measured blood sugar, hormones, organ weights, antibodies or tumours. What exists are FDA's concerns about the molecule, laboratory findings for the MGF tail peptide, experience with other PEGylated medicines, and unverified personal accounts. [2], [1]

FDA's assessment, written for compounding pharmacies, says compounded drugs containing PEG-MGF “may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization”, and that it “has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration”. Immunogenicity means the chance of provoking an immune reaction; API characterization means confirming exactly what the active ingredient is. [2]

“Research use only” describes how a product is sold; it is not a safety assessment.

Could PEG-MGF cause cancer or feed a tumour?

Nobody knows, and there are no data on PEG-MGF itself. The concern comes from laboratory work on the human MGF tail peptide:

• Prostate. The IGF-1Ec form (MGF) was found more often in prostate cancer and precancerous tissue than in normal prostate, and a synthetic MGF tail peptide made prostate cancer cells grow faster in a dish, independently of the IGF-1 receptor. When prostate cancer cells made extra tail peptide, their tumours grew faster in mice, and normal prostate cells engineered the same way spread more often. [27], [94]
• Breast. The synthetic human tail peptide increased the growth of one type of breast cancer cell (hormone-responsive MCF-7 cells) but not another, and MCF-7 cells engineered to make extra tail peptide grew and moved faster. [28]
• Mature IGF-1. In the UK Biobank study of 394,388 people followed for about 7 years, higher blood IGF-1 was linked with modestly higher rates of colorectal, breast, prostate and thyroid cancer (8–18% higher risk per 5 nmol/L). That is the body's own IGF-1, and since the MGF peptide does not act like IGF-1 at its receptor, these figures do not transfer to PEG-MGF. [95], [92]

A 2026 medical review describes these as “biologically plausible but unproven mitogenic concerns”, meaning a possible push on cell growth that has not been shown in people. A current or past cancer is a strong reason for caution. [36]

Can the PEG part cause reactions?

Possibly; it has not been studied for PEG-MGF. FDA singles out immune reactions as a concern. Evidence from other PEGylated medicines, which are different drugs given in different amounts, shows what can happen:

• Anti-PEG antibodies. In two six-month trials of pegloticase, a PEGylated gout medicine given into a vein, 40% of patients (67 of 169) developed antibodies against PEG, and loss of the drug's effect came before 44 of 56 infusion reactions. [96]
• Severe allergic reactions. In trials of pegvaliase, a PEGylated enzyme injected daily for the metabolic disease phenylketonuria, 12 of 261 participants had reactions meeting the criteria for anaphylaxis, a severe allergic reaction. [97]
• Not every PEG worry holds up. An investigation of rare severe allergic reactions to mRNA COVID-19 vaccines, which contain PEG, did not find anti-PEG IgE antibodies to be the main cause. [98]
• Tissue changes with large PEG. A European Medicines Agency paper tied small fluid-filled spaces (vacuoles) in brain-lining cells in animal studies to proteins carrying PEG of 40 kDa or more. PEG-MGF's chain is about 1.9 kDa, and no tissue studies exist for it. [80], [1]

What about the heart and blood sugar?

• Heart. The heart studies of MGF peptides were designed to find protection after a heart attack, but one study in healthy mice found harm. Two modified, non-PEGylated versions of the tail peptide given for two weeks weakened the heart's pumping and filling at both the lowest (2.25 mg/kg a day) and the highest (9 mg/kg a day) doses, while the middle dose had opposite effects depending on the version. These are not PEG-MGF and not human doses, but they show that the tail peptide can change heart function in healthy animals. [85]
• Blood sugar. No study has measured blood sugar with PEG-MGF. Low blood sugar is a known effect of IGF-1 drugs (see the IGF-1 LR3 guide), and it appears in personal accounts mainly when PEG-MGF was combined with them: one person using both PEG-MGF and IGF-1 DES reported feeling “kinda hypo for a couple hours”, and another felt a sugar drop without checking a reading. [99], [42]

What side effects have people reported?

Without human studies, the reports come from personal accounts and are not verified: injection pain (severe for one person, none for another), feelings of low blood sugar when PEG-MGF was combined with other IGF drugs, and one person who stopped because of unspecified “side effects”. [65], [99], [100]

In community education groups, members described facial water retention that settled within days, marked muscle soreness that one member suspected was caused by PEG-MGF, and stinging from acetic acid. No member reported low blood sugar, allergic reactions or problems after stopping, but about 20 users is far too few to show that something does not happen.

Could product quality change the risk?

Yes, perhaps more than for most peptides. No laboratory has published an analysis of a product sold as PEG-MGF, and the patent construct is the only described version. [1] What anti-doping laboratories have found in related products:

• Two black-market “MGF” products contained a version with a capped (amidated) end rather than the natural peptide. [29]
• Confiscated vials contained an MGF variant with one amino acid swapped, found alongside BPC-157. [30]
• A “full-length MGF” sold to athletes was a roughly 12,265-dalton protein related to IGF-1Ec, a much larger molecule than the peptide. [101]
• Only 9 of 17 black-market “follistatin 344” products contained follistatin; some of the others contained growth peptides, including MGF. [102]

FDA's concern about “API characterization” reflects the same problem: confirming exactly what the active ingredient is. In community education groups, nobody reported having a vial independently tested, and one member could not tell what a vial contained. [2]

Is PEG-MGF legal? Is it FDA-approved?

Checked September 24, 2026. Rules differ by country and change.

United States. PEG-MGF is not an FDA-approved medicine. The regulatory record so far:

• April 2020. FDA's warning letter to a Kentucky compounding pharmacy listed PEG-MGF among ingredients that “have not been nominated for inclusion on the 503A bulks list”, so products compounded from them did not qualify for the legal exemptions pharmacies rely on. [103]
• September 29, 2023. FDA placed “Mechano Growth Factor, Pegylated (PEG-MGF)” in Category 2 of its list of bulk ingredients nominated for compounding: substances that raise significant safety concerns. Plain MGF went into Category 3, nominated without adequate support. [9]
• By April 2026. FDA's safety-risk page lists PEG-MGF under “bulk drug substances nominated but withdrawn”, meaning the nominator withdrew it from Category 2. Plain MGF remains in Category 3 (list updated May 14, 2026). [2], [104]
• Before the end of February 2027. FDA's Pharmacy Compounding Advisory Committee is due to discuss whether PEG-MGF should go on the list of ingredients pharmacies may use, together with LL-37, GHK-Cu, dihexa and melanotan II. No date or materials had been posted when we checked. An advisory committee gives non-binding advice; it is not an FDA approval. [10]

Canada. No authorized product contains MGF or PEG-MGF: Health Canada's Drug Product Database returned no product for “mechano”, “MGF” or “PEG-MGF”. In April 2026 Health Canada warned people not to inject peptides bought online, stating that peptides “are generally regulated as prescription drugs” in Canada and that research-use labelling “does not make these products legal or exempt from regulatory requirements”. The advisory does not name MGF. [105], [106]

Australia. Insulin-like growth factors are prescription-only (Schedule 4) medicines and are listed among substances that are illegal to possess without authority. MGF is not named in the Poisons Standard, but in a 2013 warning letter to a supplier the Therapeutic Goods Administration (TGA) stated that “PEG MGF is a variant of insulin-like growth factor (IGF)” and identified it as a prohibited import. [107], [108]

European Union and United Kingdom. No authorization of PEG-MGF was found, and we found no statement from the European Medicines Agency or the UK medicines regulator that names it. In sport it is covered by the ban below.

A “research use only” label does not make a product legal to sell or use as a medicine.

Is PEG-MGF banned in sport? Does it show up on a drug test?

Yes, it is banned at all times. The World Anti-Doping Agency's 2026 Prohibited List, and the 2027 list that takes effect on January 1, 2027, name “mechano growth factors (MGFs)” in category S2.3, banned in and out of competition. MGF has been treated as prohibited since 2005. [11], [109], [101]

Anti-doping laboratories have added human MGF and the stabilized “Goldspink” MGF to validated blood and urine screening methods for peptides, and a WADA-funded project identified breakdown products of several MGF analogues. No study has measured how long PEG-MGF stays detectable after an injection in people. Sanctions have followed: in Australia, a cyclist received four years, plus another four for breaching the ban, for violations that included mechano growth factor. [110], [111], [112], [113]

Who should be especially cautious?

These groups have no safety data in people. For some, the findings above are a specific reason for concern.

• A current or past cancer, especially prostate or breast cancer, because the MGF tail peptide stimulated these cancer cells in laboratory studies. [27], [28]
• Heart disease, because modified tail peptides weakened heart function in healthy mice at some doses. [85]
• A history of allergy to PEG-containing medicines, because of the immune concerns FDA raises. [2]
• Pregnancy and breastfeeding. No data exist in any species.
• Under 18. No studies include young people. This guide is written for adults.
• Diabetes, or anyone taking insulin or other blood-sugar-lowering medicines, especially when combining PEG-MGF with IGF-1 LR3 or other IGF drugs; see the next question.
• Competitive athletes, military personnel and anyone tested for drugs. It is banned in sport at all times. [11]

Has PEG-MGF been tested alongside other medicines?

Not in people or animals. No study reports how PEG-MGF interacts with any prescription medicine, supplement or other peptide. [2] In practice, almost everyone who describes using it combines it with other compounds: IGF-1 LR3, growth-hormone-releasing peptides such as CJC-1295 and ipamorelin, healing peptides such as BPC-157 and TB-500, testosterone, and GLP-1 weight-loss medicines. [38], [114], [115]

The main theoretical concern is stacking several drugs that act on the same growth system. IGF-1 drugs such as IGF-1 LR3 can lower blood sugar (see the IGF-1 LR3 guide), and growth-hormone-releasing peptides act on the same hormone system; adding a peptide with unknown effects makes the result harder to predict, and harder to trace if something goes wrong. Community education groups disagree here too: some courses call PEG-MGF and IGF-1 LR3 complementary, while another warns against adding high-dose IGF-1 LR3 to PEG-MGF. Bring a complete list of everything you take to a pharmacist or doctor.

What should be monitored while using PEG-MGF?

There is no official monitoring plan, because no regulator has approved PEG-MGF or written a label for it, and no human study has measured anything after giving it. What exists is a record of what the animal studies measured, plus checks that follow from the concerns above. It can help you prepare questions for a clinician; it is not a personal testing plan.

What did the animal studies measure?

The PEG-MGF and MGF peptide studies tracked muscle force in mice, nerve-cell survival in gerbils, heart function by ultrasound or pressure measurements in sheep and mice, and markers of cell death and scarring. None measured blood sugar, IGF-1, antibodies against PEG, organ weights or tumours after PEG-MGF, and none followed animals after the last dose. [1], [53], [85], [45]

Can a blood test show whether PEG-MGF is working or present?

No routine test can. A standard IGF-1 blood test measures mature IGF-1, and whether PEG-MGF changes it, or registers on it, has never been measured. In community education groups, some say PEG-MGF does not show up on an IGF-1 test; that has never been tested. Only anti-doping laboratories, using mass spectrometry, have methods designed to detect MGF peptides. [110]

Which signals matter, and why?

These rows show what researchers and regulators flagged, not what a person will experience. Discuss any testing with a clinician. [2], [96], [85], [27]

What do people in public communities report?

Public discussions of PEG-MGF are a mix of strong praise, shrugs and scepticism. Almost none can be read on their own terms, because the people posting were nearly always using several drugs at once and none had their product tested. The most useful accounts say what else was going on and come back with an update. [37], [65]

What do the positive reports look like?

The most common positive description is faster recovery: less soreness and the ability to train the same muscle again sooner. One person said PEG-MGF was “incredible for recovery” and let them retrain their chest two days later without soreness; another used it on leg days during a steroid cycle and liked it “for the recovery”. [37], [24]

Injury stories are the other large group. People describe wrists that improved after 18 months of pain (followed by a course of IGF-1 LR3 and continued self-directed rehabilitation), injured knee tendons (“it healed them very effectively”), and help with nagging tendon problems after a hip replacement, described as “not a miracle drug, just an adjunct”. Another person said they had better results with PEG-MGF than with BPC-157 or TB-500 after many surgeries, including joint replacements. [41], [42], [116], [117]

Muscle-growth reports are more modest: “very slight” extra growth at the injection site, or some muscle regained alongside testosterone and another growth-hormone peptide. [118], [51]

Does everyone notice a difference?

No, and nonresponse is a large part of the public record. People describe “didn't notice much” after a couple of cycles of MGF (the type was not stated), no benefit at all, recovery without faster growth, and “no crazy quick gains or strength”. One commenter summed up a common view that “most people feel like they get nothing from it”. [119], [65], [120] Others said they had not used it consistently enough to judge, or that the cost was not worth the small effect. [121], [118]

The same split appears in community education groups, where some call PEG-MGF an underrated healing peptide and others say results are mixed or that it disappoints compared with IGF-1 LR3. Without a tested product, nonresponse cannot be separated from an inactive vial.

How long did the effects last?

Follow-ups are rare. One person who injected on most days said the effect faded after about two weeks and that their training suffered for two to three weeks after stopping. [77] Most other accounts stop before the course ends.

What about unwanted effects?

• Injection pain. Reports range from “hurts like hell” to no pain at all; injecting into small muscles such as the biceps was described as uncomfortable. [65]
• Low-sugar feelings, mainly alongside other IGF drugs. [99], [42]
• Unspecified side effects that made one person stop. [100]

In community education groups the reported harms were facial water retention, marked soreness and acid sting, as described in the risks section. These are personal accounts: they cannot show how often an effect occurs or that PEG-MGF caused it.

Why are these stories so hard to interpret?

Four problems appear again and again:

• Stacking. Almost every account includes other peptides, growth-hormone drugs, testosterone or steroids, and increasingly a GLP-1 weight-loss medicine. In community education groups, every member who reported using PEG-MGF combined it with other compounds. [38], [115]
• Unknown products. Nobody tested a vial, and some reports do not say whether their “MGF” was PEGylated. [119]
• Units. Amounts were given in syringe units without the concentration, or in mg when mcg was meant. [24], [25]
• Injuries heal anyway. Most injury stories include physical therapy, rest, time and other treatments, and compare one injury with a different earlier one.

A few voices dominate. In community education groups, one member accounted for 18 of the 44 reports of use, so the number of posts is not the number of people.

How can you judge a recovery story?

Useful questions to ask: What exactly was used, how much, and for how long? What else changed at the same time, including training, rehabilitation and other drugs? Was anything measured, such as strength, range of motion or a scan? And what happened weeks after stopping? Less soreness, a “pump”, a healed injury and new muscle are different outcomes.

These selected discussions are not a survey of all users. They cannot give a response rate, an average benefit or a safe dose.

How does PEG-MGF compare with IGF-1 LR3, Follistatin-344 and MK-677?

These compounds are discussed together for muscle growth and recovery, sold by the same suppliers and often combined. The table compares what each one is and how much human evidence exists. The route column describes how each is used in studies or on protocol websites, not tested doses.

The real differences are in how each one acts and how much it has been tested. IGF-1 LR3 delivers an IGF-1 signal directly; MK-677 works upstream by raising the body's own growth hormone and IGF-1 and is the only one tested against a placebo in people; follistatin blocks a growth brake; and PEG-MGF's peptide does not switch on the IGF-1 receptor at all in cell tests. No study has compared PEG-MGF with any of them. [92]

Common questions about PEG-MGF

Is PEG-MGF the same as natural MGF or IGF-1?

No. Natural MGF is a version of the IGF-1 gene's message that muscle makes after loading or damage; PEG-MGF is a synthetic copy of only the last 24 amino acids of that version's tail, with protective changes and a PEG chain added. It does not contain mature IGF-1, and in cell tests the MGF tail peptide did not activate the IGF-1 receptor. Evidence about the body's own MGF after exercise is not evidence for injected PEG-MGF. [3], [1], [92] See what PEG-MGF is.

Is PEG-MGF a steroid or a growth hormone?

Neither. Anabolic steroids are ring-shaped molecules that act on hormone receptors inside cells, and growth hormone is a much larger protein from the pituitary gland. PEG-MGF is a short chain of 24 amino acids with a polymer attached, based on a piece of the IGF-1 gene's product. It is banned in sport in its own category, as a growth factor. [1], [11] See how it might work.

How long does PEG-MGF take to work?

There is no reliable answer. No study has measured any effect in people. In personal accounts, some describe less soreness within days, others slight changes after several weeks, and many notice nothing. Those reports involve different products, amounts, training and other drugs, so they cannot give an expected timeline. [37], [118], [119] See what people report.

How long does PEG-MGF stay in your system?

Nobody knows. Its half-life has never been measured in a person or a living animal. The only data come from a patent's test tube, where the modified peptide was still detectable in human plasma after 24 hours while the unmodified peptide largely disappeared within 30 minutes. The “48–72 hour” figure on websites is an estimate, not a measurement. [1], [12] See the half-life evidence.

Does PEG-MGF show up on a drug test?

Anti-doping laboratories have validated blood and urine methods that include human MGF and the stabilized “Goldspink” MGF, and they have identified breakdown products of MGF analogues. How long PEG-MGF itself stays detectable after an injection has not been published. MGFs are banned in sport at all times, and an Australian cyclist has been sanctioned for violations that included mechano growth factor. [110], [112], [113] See sport rules.

Can you take PEG-MGF with IGF-1 LR3, BPC-157 or TB-500?

These combinations are common but have never been studied. Forum protocols have long alternated PEG-MGF with IGF-1 LR3 on different days, and injury “recovery stacks” add BPC-157 and TB-500. Community education groups disagree about pairing it with IGF-1 LR3: some courses call the two complementary, while another warns against adding high-dose IGF-1 LR3. Stacking also makes it impossible to tell which compound caused a benefit or a side effect. [22], [114], [44] Read the guides to IGF-1 LR3, BPC-157, TB-500 and the BPC-157 and TB-500 blend, and see interactions.

Does PEG-MGF build new muscle fibres?

No study shows that. The claim of new fibres (hyperplasia) is repeated online, but the MGF gene-transfer experiment behind the “20–25% growth” figure found larger fibres and no increase in fibre number, and no study of any MGF peptide has shown new fibres forming. [40] See how it might work.

Is it legal to buy PEG-MGF?

It depends on where you live. It is not an approved medicine in the United States, where FDA has cited a pharmacy for compounding with it and an advisory committee is due to discuss it; in Australia the TGA treats it as a variant of insulin-like growth factor, a prescription-only substance. [103], [10], [108] A “research use only” label does not make an unauthorized product legal to sell or use as a medicine. [106] See the dated legal-status summary.

Glossary

Plain explanations of the route, dosing and research terms used in this guide. Underlined terms in the text link here.

Adverse event

A harmful or unwanted medical event reported after someone used a treatment. A report alone does not prove the treatment caused it.

Amino acid

A small chemical building block. Chains of amino acids make up peptides and proteins. PEG-MGF's peptide is 24 amino acids long.

Animal study

Research in animals such as mice, gerbils or sheep. It shows what a substance does in a living body, but results in people can differ.

Bacteriostatic water

Sterile water containing a small amount of benzyl alcohol to slow bacterial growth, often used to mix peptides.

Bioavailability

How much of a dose reaches the bloodstream in a usable form. It depends heavily on the route. It has never been measured for PEG-MGF.

Cell study (in vitro)

Research on cells grown in a dish. It gives early clues about biology, but it is far from proof of benefit in people.

Compounding

When a pharmacy prepares a customized medicine from individual ingredients. In the US, FDA lists which bulk ingredients pharmacies may use and which raise safety concerns.

Controlled trial

A study that compares people given a treatment with a similar group given a placebo or another treatment. Randomized, placebo-controlled trials give the most reliable answers. None has tested PEG-MGF.

Course and cycle

A course is the period of repeated use, such as six weeks. A cycle is a course plus a planned break before any further use.

Daily and weekly total

All the amounts given in one day or one week, added together. For example, 200 mcg three times a week is a 600 mcg weekly total.

Dalton (Da, kDa)

A unit for the mass of a molecule. One kilodalton (kDa) is 1,000 daltons. The MGF peptide is about 2.9 kDa, and PEG-MGF about 5 kDa by calculation.

Dose (amount each time)

The amount given on one occasion. A protocol lists both the dose and how often it is given.

E peptide

The tail piece at the end of the IGF-1 precursor protein, normally cut off when mature IGF-1 is released. MGF peptides copy the last 24 amino acids of MGF's E peptide.

FDA

The US Food and Drug Administration, which approves medicines and oversees pharmacy compounding.

Freeze-dried (lyophilized)

Dried by freezing and removing the water, leaving a powder. PEG-MGF is sold this way and mixed with liquid before use.

Gene transfer (plasmid)

Delivering a gene into cells so they make a protein themselves. A plasmid is a small ring of DNA used to carry the gene. The MGF muscle-growth figure came from gene transfer in mice, not from a peptide.

GLP-1 medicines

Medicines such as semaglutide and tirzepatide that act like the gut hormone glucagon-like peptide-1. They reduce appetite and are used for diabetes and weight loss.

Growth hormone (GH, HGH)

A hormone made by the pituitary gland that prompts the liver and other tissues to make IGF-1. HGH usually means a growth-hormone medicine.

Half-life

The time it takes for the measured level of a substance in the blood to fall by half. It is not the same as how long an effect lasts. It has never been measured for PEG-MGF in a living animal or person.

Hypertrophy and hyperplasia

Hypertrophy is growth of existing muscle fibres; hyperplasia is the creation of new ones. No study has shown any MGF peptide causing hyperplasia.

IGF-1 (insulin-like growth factor 1)

A growth signal made mainly in response to growth hormone. It helps tissues grow and also lowers blood sugar, partly like insulin.

IGF-1 receptor

The docking site on cells that IGF-1 activates. In cell tests, the short MGF peptide did not activate it.

Immunogenicity

The chance that a substance provokes an immune response, such as antibodies or an allergic reaction. FDA lists it as a concern for PEG-MGF.

Intramuscular (IM)

Injected into a muscle.

Intravenous (IV)

Given directly into a vein, so it enters the bloodstream immediately.

Investigational

Still being studied and not approved by a regulator to treat any condition. PEG-MGF has not been studied in people at all.

Mass spectrometry

A laboratory method that identifies molecules by weighing them very precisely. Anti-doping and quality-testing laboratories use it to detect peptides such as MGF.

mcg and mg

Micrograms and milligrams. 1 mg equals 1,000 mcg. PEG-MGF amounts are usually written in mcg, and writing mg by mistake makes a thousand-fold error.

MGF (mechano growth factor)

A version of IGF-1 that muscle makes after being stretched or damaged, called IGF-1Ec in people. The name is also used for the synthetic 24-amino-acid peptide copied from its tail.

PEGylation

Attaching a chain of polyethylene glycol (PEG), a water-loving polymer, to a drug molecule to slow its breakdown and clearance. PEG-MGF's chain is about 1.9 kDa, small compared with many PEGylated medicines.

Pharmacokinetics

How the body absorbs, moves, breaks down and removes a substance. No pharmacokinetic study of PEG-MGF exists.

Placebo

A dummy treatment with no active ingredient, used as a comparison in studies.

Preclinical research

Studies done before research in people: cell studies and animal studies. All PEG-MGF research is preclinical.

Reconstitution

Mixing a freeze-dried powder with a liquid so it can be measured and injected. The amount of liquid sets how much peptide each unit holds.

Research use only

A label on products sold for laboratory research. It does not mean a product is approved, tested for human use or legal to sell as a medicine.

Satellite cells

Muscle stem cells that sit on the surface of muscle fibres and multiply to repair them after damage.

Schedule 4 (Australia)

Australia's prescription-only medicine category. Insulin-like growth factors are listed there.

Splice variant

One of several versions of a protein made from the same gene when its message is cut and joined in different ways. MGF is a splice variant of the IGF-1 gene.

Subcutaneous (SC)

Injected into the fatty layer just under the skin. Most PEG-MGF protocol descriptions use this route or injection into a muscle.

Syringe units

Markings on an insulin syringe that measure volume. On a U-100 syringe, 100 units equal 1 mL. The amount of drug per unit depends on the vial's concentration.

Titration

Adjusting a dose in steps, usually starting lower and increasing if needed.

WADA

The World Anti-Doping Agency, which publishes the list of substances banned in sport.

Withdrawal and rebound

Withdrawal effects are symptoms caused by stopping a substance. A rebound is a problem returning worse than before after stopping. Neither has been studied for PEG-MGF.

Explore more of the research

Go deeper into the experiments behind the claims. Across this guide, the citations include 42 original scientific papers, of which 35 are animal, cell or laboratory-testing studies and 7 are human studies that measured the body's own MGF or related medicines, not PEG-MGF. The library below groups the MGF experiments by question and names the molecule each one used. Several come from the same research groups, so paper counts are not counts of independent teams.

How this guide was researched

This guide is built from a thorough review of the sources cited throughout it: published scientific studies, a patent, trial registries, regulatory documents and published protocol descriptions. We also reviewed public online forums and community education groups where people describe their own experiences with PEG-MGF.

The guide cites 129 sources, including 42 original scientific papers. Each type of source answers a different question. Studies show what researchers measured. Protocol descriptions show how PEG-MGF is typically used. Personal accounts show what individual people experienced. Every numbered citation links to its entry below, labeled by source type.

How this guide was made

Research and drafting were AI-assisted. Every cited source was checked against the original, and the guide was reviewed and edited by Doserly before publication. It has not had an independent clinical review, and Doserly does not currently have medical reviewers. Doserly makes a medication and health-tracking app and runs Doserly Academy, both of which are promoted in this guide. Read our editorial policy for how guides are researched, updated and corrected.

This guide is for educational purposes. It summarizes what the reviewed sources report so the research is easier to understand; it is not medical advice. For a deeper dive, or to check any point for yourself, go straight to the cited sources.

Explore the sources