PEG-MGF is a pegylated version of mechano growth factor (MGF), a splice variant of IGF-1. No study of PEG-MGF itself has been published. The best-known mouse result came from a gene plasmid. FDA flags an immunogenicity risk for compounded PEG-MGF. WADA bans MGFs at all times.
This page covers what MGF is, what the animal and cell studies found, where the evidence breaks down, and where PEG-MGF stands with FDA and WADA. It lists no doses and no injection steps.
Quick takeaways
| Topic | What the sources say |
|---|---|
| What it is | Sold as the 24-amino-acid MGF peptide with polyethylene glycol attached (1, 2) |
| Best animal result | 25% larger mouse muscle fibers within 3 weeks after one injection of an MGF gene plasmid (1) |
| Human data | No human trial. Human findings are mRNA measurements in biopsies and cell cultures (3, 2) |
| Replication | Two pharma labs could not reproduce MGF’s effect on muscle cells (4) |
| FDA | Listed among withdrawn nominations, with a stated immunogenicity risk (5) |
| WADA | S2, prohibited at all times (6) |
What PEG-MGF is
MGF is a splice variant of the IGF-1 gene, called IGF-1Ec in humans and IGF-1Eb in rodents (1). The gene sits on chromosome 12 (7). In humans, a 49-base insert shifts the reading frame and gives the variant a different 24-amino-acid C-terminal peptide (2).
Goldspink and colleagues identified the mRNA in 1996 (8). They named it mechano growth factor because stretch and loading switch it on (1).
PEG-MGF is sold as that 24-amino-acid peptide with polyethylene glycol attached. PEGylation is a technique that prolongs how long a protein drug circulates (9). No published study tests PEG-MGF itself.
The mouse result everyone quotes
The 25% figure comes from Goldspink’s 2005 review. An MGF cDNA was inserted into a plasmid with muscle-specific regulatory sequences. After one injection into mouse muscle, mean fiber cross-sectional area rose 25% within three weeks. The same review says IGF-1Ea, delivered by an adenoviral vector, took four months to raise it 15% (1).
The review cites a US patent by Goldspink and Yang for the 25% result (1). A patent doesn’t go through peer review.
That was a gene construct, so the muscle made MGF itself. It says nothing about an injected, pegylated peptide.
What the animal and cell studies found
| Study | Model | Finding |
|---|---|---|
| Hill and Goldspink 2003 (10) | Rat muscle damage | MGF mRNA rose rapidly, then declined within days. IGF-1Ea rose later |
| Yang and Goldspink 2002 (11) | Cultured mouse myoblasts | The MGF E domain inhibited terminal differentiation and increased proliferation |
| Kandalla 2011 (2) | Human satellite cells | The E peptide extended proliferative lifespan in neonatal and young-adult cells but not old-adult cells |
| Hameed 2003 (3) | 8 young and 7 older men | After knee-extension exercise, MGF mRNA rose in the young men but not the older men. Resting MGF was about 100 times lower than IGF-1Ea |
| Deng 2011 (12) | Osteoblast-like cells, 27 rabbits | The E peptide was 1.4 times more pro-proliferative than IGF-1 in cells and promoted healing of a bone defect |
| Dłużniewska 2005 (13) | Gerbils, cultured hippocampal slices | The C-terminal peptide protected neurons from ischemia |
| Riddoch-Contreras 2009 (14) | ALS-model mice | An MGF plasmid improved hindlimb strength and motoneuron survival |
| Carpenter 2008 (15), Mavrommatis 2013 (16) | Sheep, mice | The E-domain peptide preserved heart function after induced infarction |
Cell studies disagree on whether the E peptide delays fusion (11) or increases it (2). Everything in this table comes from cells, rodents, rabbits, gerbils or sheep, apart from the men’s biopsies.
Where the evidence breaks down
In a paper published online in 2013, researchers at two pharmaceutical companies tried to reproduce MGF’s effect on human and mouse myoblasts. Peptide concentrations up to 500 ng/mL didn’t increase proliferation, and MGF didn’t inhibit differentiation. Primary mouse muscle stem cells didn’t respond either. The authors said the results “call in to question whether there is a physiological role for MGF” (4).
A 2010 review found that no analogous peptide product of the Igf1 gene had been identified in cells, culture medium, tissues or body fluids (17). Antibody-based studies since then report MGF immunoreactivity in tissues (19), which doesn’t show that a free peptide circulates.
A 2016 receptor assay found that full-length MGF activated the IGF-1 receptor at high concentrations, with an EC50 about nine times higher than IGF-1’s (7.83 against 0.86 nmol/L). The MGF peptide and a stabilized analog called Goldspink-MGF did not activate the IGF-1 receptor (18).
Safety and risks
No human trial of PEG-MGF or MGF has been published, so there’s no human safety record.
MGF expression is higher in prostate cancer tissue than in normal prostate. In cell culture, a synthetic MGF E peptide stimulated prostate cancer cell growth through a route that didn’t depend on the IGF-1 receptor (19). Anyone with a cancer history should talk to a clinician.
In mice, E-domain peptide variants depressed systolic and diastolic function at the lowest and highest of three doses (20). The peptides were variants of the MGF E domain. Treat this as a caution about the class.
Anti-PEG antibodies have been linked to loss of efficacy and more adverse effects with some PEGylated drugs (9). FDA names immunogenicity specifically for PEG-MGF (5).
Where PEG-MGF stands with FDA and WADA
FDA. FDA’s page, current as of 22 April 2026, lists PEG-MGF among bulk drug substances nominated for compounding but withdrawn by the nominators. It says compounded drugs containing PEG-MGF “may pose significant risk for immunogenicity for certain routes of administration,” and that FDA has identified no human exposure data for PEG-MGF by any route (5). Unpegylated MGF sits in Category 3, nominated without adequate support (21).
A law-firm summary of FDA’s April 2026 notice says removal from Category 2 doesn’t place a substance on the 503A bulks list (22). PEG-MGF isn’t an approved drug.
WADA. The 2026 Prohibited List names “Mechano growth factors (MGFs)” under S2. S2 is prohibited at all times, in and out of competition (6). Anti-doping labs have published mass spectrometric work on MGF (8).
How to judge a listing
A certificate of analysis describes one lot. For a peptide it has to show identity as well as purity. Look for these:
- Identity test. Mass spectrometry that confirms identity, not only a purity percentage.
- Batch number. It matches the number on the vial.
- Independent lab. Not the seller’s own, with a name, date and method you can look up.
- Verification. The lab lets you confirm the report on its own site.
See our best peptide vendors for seller comparisons, our best peptides ranked by human evidence guide for the wider rules, and our MGF peptide page for the unpegylated peptide.
Frequently asked questions
What is PEG-MGF?
PEG-MGF is sold as the 24-amino-acid C-terminal peptide of mechano growth factor with polyethylene glycol attached. MGF is a splice variant of the IGF-1 gene.
Does PEG-MGF build muscle in humans?
No human trial of PEG-MGF has been published. The best-known result, 25% larger mouse muscle fibers, came from an MGF gene plasmid. Two pharmaceutical labs could not reproduce MGF’s effects on muscle cells in culture.
What is the difference between MGF and PEG-MGF?
PEG-MGF is sold as the MGF peptide with polyethylene glycol attached. PEGylation is a technique that prolongs how long a protein drug circulates. No published study compares the two.
Is PEG-MGF banned by WADA?
Yes. WADA’s 2026 list names mechano growth factors under S2, which is prohibited at all times.
Is PEG-MGF approved or legal to compound?
It isn’t an approved drug. FDA lists it among bulk drug substances nominated for compounding but withdrawn by the nominators, and says compounded drugs containing it may pose significant risk for immunogenicity.
Does PEG-MGF cause cancer?
Unknown. No human study tests it. In cell culture, a synthetic MGF E peptide stimulated prostate cancer cell growth, and MGF expression is higher in prostate cancer tissue than in normal prostate.
Is MGF a natural hormone?
MGF is a splice variant of IGF-1 made in muscle after loading and damage. As of a 2010 review, the 24-amino-acid peptide itself had not been identified in cells, culture medium, tissues or body fluids. Antibody-based studies since then report MGF immunoreactivity in tissues.
This page is information, not medical advice or instructions for human use. PEG-MGF is not an approved drug.
References
- Goldspink G. Mechanical signals, IGF-I gene splicing, and muscle adaptation. Physiology (Bethesda). 2005;20:232-238. PMID 16024511.
- Kandalla PK, et al. Mechano growth factor E peptide (MGF-E), derived from an isoform of IGF-1, activates human muscle progenitor cells and induces an increase in their fusion potential at different ages. Mech Ageing Dev. 2011;132(4):154-162. PMID 21354439.
- Hameed M, et al. Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. J Physiol. 2003;547:247-254. PMID 12562960.
- Fornaro M, et al. Mechano-growth factor peptide, the COOH terminus of unprocessed insulin-like growth factor 1, has no apparent effect on myoblasts or primary muscle stem cells. Am J Physiol Endocrinol Metab. 2014;306(2):E150-E156. PMID 24253050.
- FDA. Certain bulk drug substances for use in compounding that may present significant safety risks.
- World Anti-Doping Agency. The 2026 Prohibited List, section S2.
- NCBI Gene. IGF1 insulin like growth factor 1 (Homo sapiens), 12q23.2.
- Thevis M, et al. Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls. Growth Horm IGF Res. 2014;24:276-280. PMID 25466910.
- Zhang P, et al. Anti-PEG antibodies in the clinic: current issues and beyond PEGylation. J Control Release. 2016;244:184-193. PMID 27369864.
- Hill M, Goldspink G. Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damage. J Physiol. 2003;549:409-418. PMID 12692175.
- Yang S, Goldspink G. Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Lett. 2002;522:156-160. PMID 12095637.
- Deng M, et al. Mechano growth factor E peptide promotes osteoblasts proliferation and bone-defect healing in rabbits. Int Orthop. 2011;35(7):1099-1106. PMID 21057789.
- Dluzniewska J, et al. A strong neuroprotective effect of the autonomous C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia. FASEB J. 2005;19(13):1896-1898. PMID 16144956.
- Riddoch-Contreras J, et al. Mechano-growth factor, an IGF-I splice variant, rescues motoneurons and improves muscle function in SOD1(G93A) mice. Exp Neurol. 2009;215(2):281-289. PMID 19038252.
- Carpenter V, et al. Mechano-growth factor reduces loss of cardiac function in acute myocardial infarction. Heart Lung Circ. 2008;17:33-39. PMID 17581790.
- Mavrommatis E, et al. The E-domain region of mechano-growth factor inhibits cellular apoptosis and preserves cardiac function during myocardial infarction. Mol Cell Biochem. 2013;381:69-83. PMID 23712705.
- Matheny RW, Nindl BC, Adamo ML. Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology. 2010;151:865-875. PMID 20130113.
- Janssen JA, et al. Potency of full-length MGF to induce maximal activation of the IGF-I R is similar to recombinant human IGF-I at high equimolar concentrations. PLoS One. 2016;11(3):e0150453. PMID 26991004.
- Armakolas A, et al. Preferential expression of IGF-1Ec (MGF) transcript in cancerous tissues of human prostate. Prostate. 2010;70(11):1233-1242. PMID 20564425.
- Solís C, et al. Mechano-growth factor E-domain modulates cardiac contractile function through 14-3-3 protein interactomes. Front Physiol. 2022;13:1028345. PMID 36467694.
- FDA. Bulk drug substances nominated for use in compounding under section 503A: categories 1, 2 and 3.
- Orrick. FDA announces removal of 12 peptides from Category 2 and schedules PCAC meetings.