MGF peptide (mechano growth factor): what it is, what the research shows and what is unknown

The IGF-1 gene does not produce a single product. Its pre-messenger RNA can be spliced in more than one way, and each version codes for a pro-protein made of the same 70-amino-acid mature IGF-1 plus a different tail called the E domain, which is normally cut off during processing ^{[1] [2]}. In the late 1990s Geoffrey Goldspink’s group in London found that one of these splice variants was switched on in rabbit muscle that had been stretched and electrically stimulated, and named it mechano growth factor, or MGF, because mechanical loading induced it ^[3]. In humans the variant is called IGF-1Ec; in rodents the equivalent is IGF-1Eb ^{[1] [4]}.

The product sold as MGF peptide is not the whole splice variant. It is a synthetic peptide of 24 amino acids matching the end of the IGF-1Ec E domain, sometimes written MGF-24aa-E or MGF E peptide ^{[5] [6]}. Whether this peptide exists as a separate molecule in the body is doubtful: a 2010 review in Endocrinology noted that no such peptide had ever been isolated from cells, culture medium, animal tissue or body fluids ^[2]. The E domain is unusual because a 49-base-pair insert in the human variant shifts the reading frame, giving it a sequence unlike the other IGF-1 tails ^[5].

MGF is therefore related to, but different from, IGF-1 LR3 and IGF-1 DES, which are modified versions of mature IGF-1 itself. It is also different from PEG-MGF, which is the same 24-amino-acid peptide with a polyethylene glycol chain attached. See what research peptides are for how compounds like this reach the market.

The original model, from Goldspink’s group, is that loading or damage causes muscle to express the MGF variant first, and its E domain activates satellite cells, the muscle’s resident stem cells, making them multiply before the IGF-1Ea variant takes over and drives them to fuse and repair the fibre ^{[4] [7]}. In a 2002 cell study, the synthetic E domain increased myoblast proliferation while holding back their final differentiation, and blocking the IGF-1 receptor with an antibody did not stop this, which the authors took as evidence for a separate receptor ^[6]. Human satellite cells from neonatal and young adult donors, but not from old donors, lived longer in culture and fused more readily when exposed to the peptide ^[5].

Later work from other laboratories challenged the separate-receptor idea. A 2012 study found that the E peptides increased signalling through the IGF-1 receptor by raising the amount of receptor at the cell surface, that their effects on proliferation and migration were blocked by inhibiting that receptor, and that they had little independent activity of their own ^[8]. In 2014 the same group expressed the E peptides in mouse muscle using viral vectors: the EB peptide, the rodent equivalent of MGF, produced hypertrophy that depended on the IGF-1 receptor, but the enlarged muscles were weaker ^[9].

The identity of any MGF receptor remains unknown, and the 2010 Endocrinology review listed it among the outstanding questions, alongside whether the peptide has any natural counterpart at all ^[2].

The claimed MGF peptide benefits, muscle repair, hypertrophy and faster recovery, rest on cell and animal experiments with mixed results. On the positive side, the E domain peptide increased proliferation of mouse myoblasts ^[6] and activated human muscle progenitor cells in culture ^[5]. In a gerbil model of transient brain ischaemia, the synthetic peptide protected vulnerable hippocampal neurons, and in slice cultures it was as potent as full-length IGF-1 with a longer-lasting effect ^[10]. In sheep with induced heart attacks, the E domain improved cardiac function and reduced the area of compromised muscle by 35% at eight days ^[11].

On the negative side is the most direct replication attempt. In 2014, scientists at two pharmaceutical companies tried to reproduce the claimed effects of MGF peptides on muscle cells. Concentrations up to 500 ng/mL failed to increase proliferation of the C2C12 mouse line or of primary human myoblasts, failed to inhibit their differentiation into myotubes, had no effect on primary mouse muscle stem cells, and did not activate the signalling pathway reported in cardiac myocytes, whereas mature IGF-1 and the full-length IGF-1Eb pro-protein worked in every assay. The authors concluded that the results call into question whether MGF has any physiological role ^[12].

Some of the animal work also cuts against the bodybuilding use. Viral expression of the rodent E peptide in mouse muscle increased muscle mass but at the expense of strength ^[9]. No study has tested whether injected MGF peptide builds muscle or improves recovery in any animal model of training, and none has tested it in people.

No published study has injected MGF into humans, and no trial of MGF is registered on ClinicalTrials.gov. The human research measures the body’s own MGF messenger RNA in muscle biopsies. In a 2003 study, eight young and seven elderly men did ten sets of heavy knee extensions, and biopsies 2.5 hours later showed that resting MGF mRNA was about 100-fold lower than the IGF-1Ea isoform in both groups, that exercise raised MGF mRNA in the young but not the elderly, and that IGF-1Ea did not change in either ^[13].

A 2004 study in men aged around 74 found that 12 weeks of growth hormone injections raised muscle MGF mRNA by 80%, five weeks of resistance training raised it by 163%, and the two combined raised it by 456% ^[14]. But when healthy young men with normal growth hormone levels were given two weeks of daily growth hormone in a randomised crossover trial, their circulating IGF-1 more than tripled while muscle MGF and IGF-1Ea transcripts did not change at all ^[15]. These studies show that muscle makes more of the MGF transcript in response to loading, particularly in the young. They say nothing about what happens when a synthetic 24-amino-acid peptide is injected under the skin, which is the way MGF is sold.

The only other human data come from anti-doping laboratories and are about products, not effects. Two black-market preparations sold as MGF were found in 2012 to contain a C-terminally amidated analogue of the human peptide rather than the natural sequence ^[16]. A “full-length MGF” offered to athletes was characterised in 2014 as a 12,264.9 Da protein closely related to IGF-1Ec but with a modified end, lacking its terminal lysine and carrying an arginine-to-histidine substitution ^[17]. Confiscated vials analysed in 2017 contained a variant labelled MGF R23H ^[18], and a 2019 study of products sold as follistatin found MGF in some of them ^[19].

MGF vs IGF-1 LR3 is a comparison between two different parts of the IGF-1 system. IGF-1 LR3 is the whole 70-amino-acid mature IGF-1 hormone with an extension and one substitution, designed to escape the binding proteins that normally hold IGF-1 in check; it acts through the IGF-1 receptor and lowers blood sugar strongly in animals. MGF is a short piece of the E domain that is cut off from the pro-protein, and whether it acts through the IGF-1 receptor or a separate one is disputed ^{[6] [8]}. Neither has published human trials. Forum protocols that combine the two, on the theory that MGF “primes” satellite cells before IGF-1 makes them fuse, are an extrapolation from the splicing model ^[4] and have never been tested.

MGF vs PEG-MGF is a comparison between the same peptide with and without a polyethylene glycol tag. Unmodified small peptides are cleared quickly, and the tag is intended to keep the peptide in circulation longer. Our PEG-MGF guide explains that no study of the PEGylated version has been published in any species. The claimed half-life difference, minutes for MGF and days for PEG-MGF, has not been measured for either.

All published doses are from cells and animals, and most were applied directly to tissue rather than injected systemically. Cell studies used nanogram-per-millilitre concentrations, up to 500 ng/mL in the negative replication study ^[12]. In sheep with induced heart attacks, 200 nM of the E domain was delivered to the heart ^[11]. Gerbils with brain ischaemia were treated with the synthetic peptide, with protection of hippocampal neurons as the outcome ^[10]. Mice received the E peptide by viral gene delivery into muscle, not by injection of peptide ^[9].

No human dose has ever been tested, so there is no evidence-based MGF peptide dosage for muscle growth or recovery. The 200 to 400 µg doses injected into trained muscles after workouts that appear on forums are not drawn from any study, and the idea of injecting MGF locally rests on a model of how muscle expresses its own transcript ^[4], not on evidence about where an injected peptide goes. For the arithmetic of mixing a vial, a 2 mg vial in 1 mL of bacteriostatic water gives 2 mg per mL, so each unit on a U-100 insulin syringe holds 20 µg; the peptide calculator and the MGF calculator page handle other volumes. These are calculations, not recommendations.

MGF is sold as a freeze-dried powder for injection, usually in 2 mg or 5 mg vials. Because the 24-amino-acid peptide has no measured human pharmacokinetics, claims about its half-life are guesses. Unmodified peptides of this size are typically broken down within minutes, which is the rationale for the PEGylated version and for the “full-length MGF” protein that has appeared on the black market ^[17]. Both the C-terminally amidated analogue and the R23H variant found in seized products are modifications that would be expected to change stability ^{[16] [18]}.

Some sellers list oral or nasal MGF. We found no study of MGF given by any route other than injection, local tissue delivery or viral gene expression.

There are no human safety data for MGF. The animal literature offers two cautions. First, sustained expression of the rodent E peptide produced muscle that was bigger but weaker ^[9], which is the opposite of what users hope for. Second, the E peptide increases signalling through the IGF-1 receptor ^[8], and IGF-1 signalling promotes cell growth; a 2026 review of growth hormone-axis peptides described mitogenic concerns about IGF-1 analogues as biologically plausible but unproven, and listed dysglycaemia, fluid retention and joint and muscle pain among adverse effects reported across the class ^[20]. Interestingly, one cell study suggested the MGF peptide might avoid the oncogenic effects of IGF-1 itself ^[5], but this has not been tested in animals.

The products themselves are the most concrete risk. Analyses of black-market MGF have found amidated analogues ^[16], a modified full-length protein ^[17], and an R23H variant ^[18], none of which has any biological data. Whether these variants are immunogenic is unknown. A 2026 review of peptides sold in sports medicine noted that rigorous human safety data are scarce across the class and that there is potential for serious harm ^[21].

MGF is not approved as a medicine anywhere, and no company has taken it into clinical development. In sport, WADA has considered MGF and its analogues prohibited since 2005 ^[17], and the 2026 Prohibited List covers growth factors and related substances that affect muscle protein synthesis under section S2, prohibited at all times ^[22]. Anti-doping laboratories have published methods to detect the synthetic peptide, the amidated analogue and the full-length protein at concentrations below 1 ng/mL ^{[16] [17] [23]}. UK Anti-Doping applies the same list ^[24].

In the UK, MGF has no marketing authorisation, and regulation 46 of the Human Medicines Regulations 2012 makes selling or supplying an unauthorised medicinal product an offence ^[25]. It is not a controlled drug under the Misuse of Drugs Act 1971, whose peptide hormone entries name somatropin and chorionic gonadotrophin but not IGF-1 or its variants ^[26]. See our UK legal status page, the US page and the legal status overview for how research peptides are treated elsewhere.

MGF is supplied as a freeze-dried powder. Like other peptides it should be kept cold, dry and away from light, and refrigerated once reconstituted. Its short expected life in solution makes prompt use after mixing more important than for stable peptides. See how to store peptides.

PepFinder does not sell MGF. You can compare MGF prices, including UK listings and US listings, and filter for third-party tested suppliers.

Identity testing matters more than usual here because three different analogues have turned up in products sold as MGF ^{[16] [17] [18]}. A certificate of analysis for the 24-amino-acid peptide should show a mass spectrum matching the human E domain sequence, not an amidated or substituted version, and a purity figure by HPLC on its own does not tell you which molecule is in the vial. Read how to read a COA, third-party peptide testing and how to spot a fake peptide supplier. If muscle growth is the aim, our peptides for muscle growth page compares MGF with GDF-8 (myostatin) inhibitors and other compounds that have actually been studied in people.