MGF

Origin and structure

In 1996 Geoffrey Goldspink's group at the Royal Free Hospital School of Medicine in London stretched rabbit muscle and found that the growing muscle made a second form of IGF-1 messenger RNA besides the usual one. Alternative splicing had added a short insert, 52 base pairs in rabbits and rodents and 49 in humans, which shifts the reading frame and gives the end of the precursor protein, the E-domain, a different sequence. The variant was later named mechano growth factor, because mechanical load switched it on. In humans it is called IGF-1Ec; in rodents the matching form is IGF-1Eb.

All IGF-1 variants carry the same 70-amino-acid mature hormone; they differ only in the E-domain tail, which is normally cut off. In humans the IGF-1Ec tail is 40 amino acids long, and most laboratory work used a synthetic copy of its last 24, which in the human sequence reads YQPPSTNKNTKSQRRKGSTFEERK. A 2010 review in Endocrinology pointed out that no such free peptide had ever been isolated from cells, tissues or body fluids, so MGF the peptide is a construct modelled on the gene rather than a hormone shown to circulate.

PEG-MGF is sold as a version with polyethylene glycol (PEG) attached, a common way to slow the breakdown of a drug. Its exact structure has not been published, and a 2026 review in Frontiers in Endocrinology found no reported half-life and no peer-reviewed human study.

How it is thought to work

The idea comes from injured muscle. After damage the MGF transcript rises first, in step with markers of dividing satellite cells, the muscle's stem cells, and the ordinary IGF-1Ea transcript follows later as new fibres mature. Goldspink's group proposed that the tail peptide is a separate signal telling satellite cells to multiply before they fuse into fibres, and in their cell studies the synthetic peptide increased the proliferation of muscle cells and delayed their fusion. A group working on prostate-cancer cells later reported that, in those cells, the peptide's growth effect did not need the IGF-1 receptor.

That picture has been challenged. In 2014 scientists at two pharmaceutical companies, one of them Novartis, tried to reproduce the core claim and could not: at concentrations up to 500 ng/ml the MGF peptide did not make mouse C2C12 myoblasts or primary human myoblasts multiply, while mature IGF-1 and the full-length IGF-1Eb protein did; it did not hold back their differentiation either, and it had no significant effect on primary mouse muscle stem cells. Neither the native peptide nor a stabilised version triggered the signalling response reported earlier in heart-muscle cells. The authors concluded that their results call into question whether MGF has a physiological role at all.

How long the peptide lasts in the body is unknown. Online sources say unmodified MGF breaks down within minutes and that PEG-MGF lasts much longer, but no pharmacokinetic study of either form has been published.

Is MGF approved?

No. No medicine containing MGF or PEG-MGF has been authorised by the EMA, by the Dutch Medicines Evaluation Board (CBG) or by any regulator elsewhere, and no trial in people has been registered. In the Netherlands that means it may not be sold or promoted for use in people; it circulates only as research material.

In the United States the question is pharmacy compounding, and it concerns PEG-MGF. The FDA put PEG-MGF on its list of bulk substances that may present significant safety risks. It warned of a possible risk of immune reactions with some routes of administration and of problems with peptide impurities and with characterising the active ingredient, and said it had found no human exposure data on PEG-MGF by any route. The nomination was later withdrawn; the FDA's page, last updated in April 2026, lists PEG-MGF among withdrawn nominations with the same warning.

The FDA has announced that its Pharmacy Compounding Advisory Committee will discuss PEG-MGF, together with LL-37, GHK-Cu, dihexa and melanotan II, at a meeting before the end of February 2027. No date or public docket had been published when this page was checked in October 2026. The committee's vote would be advice only, and even a compounded product would not be an approved drug.

In sport it is prohibited at all times. Class S2.3 of the WADA Prohibited List, growth factors and growth-factor modulators, names mechano growth factors (MGFs) next to IGF-1 and its analogues, and also covers other growth factors that affect muscle protein synthesis or regeneration, which takes in PEG-MGF. The Dutch anti-doping rules apply the same list, and in 2012 a doping laboratory described a mass-spectrometry signature that tells a modified black-market MGF apart from the body's own form.

What the research shows

No published study has given MGF or PEG-MGF to people, and a search of ClinicalTrials.gov in October 2026 found no registered trial that does. What exists is muscle biopsies measuring the body's own transcript, cell studies with the synthetic peptide and animal work, listed below.

• Human biopsies (Hameed et al., 2003): 8 younger (aged 25 to 36) and 7 older adults (aged 70 to 82) did 10 sets of 6 heavy knee extensions with one leg. 2.5 hours later the MGF transcript had risen in the younger group but not in the older group. At rest MGF was about 100 times less abundant than IGF-1Ea. This measured the body's own messenger RNA, not an administered peptide.
• Human muscle cells (Kandalla et al., 2011, with Goldspink as co-author): the 24-amino-acid peptide lengthened the proliferative lifespan and delayed the ageing of satellite cells from newborn and young-adult donors, but not from older adults, and increased their fusion at all ages.
• Failed replication (Fornaro et al., 2014): at up to 500 ng/ml no effect on the proliferation or differentiation of mouse or human myoblasts, and no significant effect on primary mouse muscle stem cells, while mature IGF-1 and full-length IGF-1Eb worked in the same tests.
• Heart and cell transplants (animals): in heart-attack models, local delivery of the E-domain peptide preserved heart function and reduced cell death, and the peptide improved the engraftment of transplanted muscle precursor cells. A 2026 review counts these as preclinical findings that have not been tested in people.
• Prostate cancer (cells and tissue, Armakolas et al., 2010): prostate-cancer tissue made more of the MGF transcript than normal prostate, and the synthetic peptide made prostate-cancer cells grow.
• PEG-MGF: we found no peer-reviewed study of PEG-MGF itself, in cells, animals or people; the 2026 review places it in its lowest evidence tier, with no human studies.

MGF, PEG-MGF and IGF-1: what the names mean

The name MGF covers several different things: the IGF-1Ec messenger RNA that muscle makes after loading (IGF-1Eb in rodents), the E-domain tail of the protein it encodes, the synthetic 24-amino-acid peptide based on that tail, and the products sold under the name. Findings on one do not automatically carry over to another. The biopsy studies measured the first, the cell and animal studies used the third, and the products can differ again: in 2012 a doping laboratory analysed two black-market MGF products and found that both contained a C-terminally amidated analogue of human MGF rather than the natural sequence.

PEG-MGF has no peer-reviewed literature of its own, so the case made for it borrows from work on the unmodified peptide. MGF is also not the same as IGF-1 or IGF-1 LR3: those are the mature hormone or an analogue of it, acting through the IGF-1 receptor, whereas the MGF peptide is only a piece of the tail that is normally cut off. In sport they fall under the same WADA class, S2.3.

Frequently asked questions

Is MGF legal in the Netherlands?

MGF and PEG-MGF are not registered medicines in the Netherlands or anywhere else, so they may not be sold, advertised or supplied for use in people. Trading them as research material is a different status, which our guide on research-use-only products in the Netherlands explains. For athletes under anti-doping rules they are prohibited however they were obtained.

Is MGF banned in sport?

Yes, at all times, in and out of competition. WADA class S2.3 names mechano growth factors (MGFs) among the prohibited growth factors, and the class also covers other growth factors that affect muscle repair, which includes PEG-MGF. The Dutch anti-doping rules apply the same list. See our guide on peptides and the doping list.

What is the difference between MGF and PEG-MGF?

MGF, as studied in labs, is a synthetic 24-amino-acid peptide copied from the tail of IGF-1Ec. PEG-MGF is sold as the same peptide with polyethylene glycol attached, which is meant to slow its breakdown. Neither half-life has been measured in a published study, all the research cited for MGF used the unmodified peptide, and PEG-MGF has no peer-reviewed studies of its own.

Has MGF been tested in humans?

No. No published study or registered trial has given MGF or PEG-MGF to people. The human data are muscle biopsies showing that the body's own MGF transcript rises after heavy exercise in younger adults, from a 2003 study of 15 people, and lab work on human muscle cells, with conflicting results.

Is MGF safe?

Nobody can say, because it has never been tested in people. The FDA has flagged PEG-MGF as a substance that may present significant safety risks, citing possible immune reactions, impurities and the absence of any human exposure data. Because it belongs to the IGF-1 family and made prostate-cancer cells grow in the lab, a 2026 review flags a theoretical risk of promoting cell growth that has never been studied in people.

Does exercise raise MGF?

Muscle makes more of its own MGF transcript after heavy or damaging exercise. In the 2003 biopsy study it was raised 2.5 hours after a heavy one-leg session in adults aged 25 to 36, but not in those aged 70 to 82. Whether a free MGF peptide is then released into the blood is unclear: a 2010 review found that none had ever been isolated from tissue or body fluids.

Storage and handling

Store according to product-label instructions and batch handling notes. Lyophilized research peptides are commonly kept dry, protected from light, and handled with clean laboratory technique.

References

Checked against these sources on 28 October 2026.