MGF and PEG-MGF: research, side effects and dosage in studies

In short

MGF (mechano growth factor) is the name of a splice form of the IGF-1 gene and of a synthetic peptide derived from it [1]. In humans only the muscle's own MGF production after exercise has been measured [2]B; the MGF or PEG-MGF peptide sold online has not been given to humans in any published study [17].

• The muscle's own MGF and the peptide sold online are different things. Human studies have measured whether MGF messenger RNA in muscle rises after exercise [2, 3, 4]B. The MGF sold online is a synthetic 24-amino-acid fragment, and no matching peptide has been found in the body [1].
• In cell experiments the MGF peptide increased the division of muscle precursor cells [6, 8]D, but repeat experiments by two drug companies found no effect at all [7]D.
• There is no peer-reviewed human study of PEG-MGF, and its half-life has not been reported [17].
• Modified versions of MGF have been found in black-market products [14, 15]D.
• In Finland MGF is in Annex 1 A of the medicines list, and the WADA Prohibited List names it in class S2.3 [18, 19]regulator.

What is MGF?

MGF, mechano growth factor, is a name used for two different things: one splice form of the IGF-1 gene and a synthetic peptide derived from it [1].

The IGF-1 gene produces several forms of messenger RNA. In humans MGF corresponds to the IGF-1Ec form and in rodents to IGF-1Eb; they differ from the other forms in the E part at the end [8]D. Because muscle makes more of this form after strain and damage, it was named mechano growth factor [1].

The "MGF" sold online is a synthetic peptide matching the last 24 amino acids of the E part [1] [15]D. No matching peptide has been found in cells, tissues or body fluids, so it is not known whether the body makes it at all [1].

PEG-MGF is the MGF peptide with polyethylene glycol (PEG) attached. According to sellers it is meant to make the substance last longer, but PEG-MGF has not been studied as a drug [17]. A related substance is IGF-1 LR3, another modified IGF-1. Basics: What are peptides? All substances: Peptides A-Z.

Evidence at a glance

Each cell gives the kind of study and its source. The letter is the evidence level, not the result.

"-" = no such study is known.

What is MGF studied for?

MGF is studied in two ways: in humans the muscle's own MGF is measured, and in animals and cells the synthetic peptide is tested. It has not been studied as a medicine in humans [17].

• Exercise and ageing: muscle biopsies have been used to measure whether MGF messenger RNA rises after strength or braking-type exercise in young and older people [2, 3, 4]B.
• Muscle precursor cells: the peptide's effect on the division of muscle precursor cells has been studied in cell experiments, with conflicting results [6, 7, 8]D.
• Nerves, tendons and the heart: animal experiments have been done in ALS mice [9]C, tendon injuries in rats [10]C and heart attack in sheep and mice [11, 12]C.
• Cancer: MGF production has been measured in prostate cancer tissue, and the peptide's effect on cancer cells has been studied in the laboratory [13]D.
• Doping control: doping laboratories have identified black-market MGF products and developed tests for them [14, 15]D.

How does MGF work?

How MGF works is unclear. In the first cell experiments the MGF peptide increased the division of muscle precursor cells and slowed their maturation, and the effect seemed to run through a receptor other than the IGF-1 receptor [6]D. Mature IGF-1 did not have this effect of slowing maturation [6]D.

In human muscle precursor cells the peptide extended the cells' capacity to divide in cells taken from newborns and young adults, but not in cells from older adults [8]D. In a heart-derived cell line the peptide moved quickly into the cell and its nucleus without activating the IGF-1 receptor and prevented cell death [12]D.

Two drug companies tried to repeat these findings. The peptide did not increase the division of mouse or human muscle cells, did not block their maturation and did not activate signalling pathways in heart muscle cells, although IGF-1 did all this in the same experiments [7]D.

The link with exercise rests on messenger RNA measured in humans. A rise in the muscle's own MGF does not show that an injected peptide would do the same [1].

Has MGF been studied in humans?

Not as a treatment. No MGF or PEG-MGF peptide has been given to humans in any peer-reviewed study [17]. In humans only the muscle's own MGF messenger RNA has been measured after exercise or growth hormone [2, 3, 4]B [5]A.

Strength training in young and older people (2003)

Eight young (aged 25-36) and seven older people (aged 70-82) did heavy single-leg thigh exercise sets. Muscle biopsies were taken from both thighs 2.5 hours after the exercise [2]B.

At rest there was about a hundred times less MGF messenger RNA than the main form of IGF-1. The exercise raised MGF in the young but not in the older people [2]B.

Braking-type cycling (2008)

Nine young and eight older people pedalled backwards against resistance for an hour, which loads the muscle as it lengthens. MGF messenger RNA rose in both groups [3]B. The result differs from the 2003 study, in which no rise was seen in older people [2]B.

Static exercise in women (2006)

In six healthy women MGF messenger RNA was raised 2.5 hours after static thigh exercise, and the rise lasted at least two days [4]B.

Growth hormone and exercise in young men (2009)

Seven young men received growth hormone or placebo for two weeks in a randomised crossover design. Blood IGF-1 rose clearly, but muscle MGF did not change after growth hormone or after heavy exercise [5]A.

Promising, but only in animal and cell studies

These findings come from animals or cells and have not been studied in humans. Results of animal studies and cell studies cannot be carried straight over to humans.

• Muscle precursor cells and ageing no human studies

  In human muscle precursor cells the MGF peptide extended the cells' capacity to divide and delayed their ageing in cells taken from newborns and young adults. The cells also fused into muscle fibres more readily in all age groups [8]D.

  If it held in humans: the peptide could help muscle repair and slow age-related muscle loss.

  Why it might not translate: the effect was seen in cell culture, not in a living person, and it did not show in cells from older adults. In repeat experiments by two drug companies the peptide did not increase the division of human or mouse muscle cells or block their maturation [7]D.

  Evidence now: a few cell studies, some by the same research group. We know of no human study in which MGF was given.

• Protecting nerve cells in ALS no human studies

  In a mouse model of ALS, transfer of the MGF gene into the hindlimb muscles improved muscle strength and increased motor neuron survival more than transfer of the IGF-1 gene [9]C.

  If it held in humans: MGF could slow the loss of motor nerve cells.

  Why it might not translate: the mice were not given the peptide but a gene that made the muscle produce MGF. According to the researchers, trials of IGF-1 in ALS patients have given conflicting results [9]C.

  Evidence now: one mouse study. We know of no registered human study.

• Tendon injuries no human studies

  In rats a synthetic MGF E-part peptide improved the function and stiffness of an injured Achilles tendon compared with saline [10]C.

  If it held in humans: the peptide could speed up the healing of tendon injuries.

  Why it might not translate: the study was done in rats with one injury model by one research group, and a concentration from a rat experiment cannot be converted into a human dose.

  Evidence now: one rat study. There is no human study.

• Heart attack no human studies

  In sheep the MGF E part preserved heart function after a heart attack, and there was 35% less damaged heart muscle than in controls [11]C. In mice the peptide preserved the heart's ability to contract and reduced cell death [12]C.

  If it held in humans: the peptide could limit the damage caused by a heart attack.

  Why it might not translate: in mice the peptide was given at the moment of the heart attack [12]C, and follow-up in sheep lasted only eight days [11]C. In the drug companies' repeat experiments the peptide did not activate signalling pathways in heart muscle cells [7]D.

  Evidence now: a few animal studies, partly from the same network of researchers. There is no human study.

Who studies MGF?

Research on MGF began with Geoffrey Goldspink's group in London [15]D, and Goldspink is an author on most of the exercise and cell studies [2, 3, 4]B [6, 8]D. The most critical repeat experiment was done by researchers at Novartis [7]D, and the review was written by researchers at the US Army Research Institute of Environmental Medicine [1].

Doping analytics is done at the German Sport University Cologne [15]D, the doping control laboratory of Ghent University in Belgium [14]D and Seibersdorf in Austria [16]D.

Who wrote this page: the editorial team

This page was written by the Molecular Recovery editorial team. The draft was made with the help of AI, and the claims were checked against the sources (AI policy). The page has not been medically reviewed. How we work: About us.

How long does MGF stay in the body?

Not known. No half-life of the MGF peptide or PEG-MGF in humans has been reported [17]. According to sellers, attaching PEG is meant to make the substance last longer, but it changes how the substance moves in the body so much that results with the plain peptide cannot be carried over to PEG-MGF [17].

The Cologne doping laboratory noted in 2014 that further studies would be needed on the efficacy and elimination of "full-length MGF" [15]D.

What are the side effects of MGF?

There are no research data on the harms of MGF in humans, because it has not been given to humans in studies [17]. Peptide harms more generally: side effects in studies.

A theoretical cancer risk

There was more MGF in prostate cancer tissue and its precursor changes than in healthy prostate, and healthy prostate epithelial cells in culture did not make it. In the laboratory the synthetic MGF peptide increased the growth of prostate cancer cells, independently of the IGF-1 receptor [13]D.

According to a review, this is a theoretical concern based on cells and tissues, not a harm seen in humans [17].

Reported harms of the substance class

For peptides that modify the growth hormone and IGF-1 axis and are marketed as "research chemicals", reported harms include hormonal and metabolic disturbances, fluid retention, muscle and joint pain and injection site reactions. These concern the whole group, not measurements made with MGF, and there are no human data on PEG-MGF [17].

Product contents as a harm in itself

Modified versions whose structure differs from human MGF have been found in black-market MGF products [14, 15]D. MGF has also been found in products whose label named a completely different substance [16]D.

Interactions and who has no data

There are no data on interactions with other medicines, and none on pregnancy, breastfeeding or children, because there are no human studies [17]. MGF has not been given to people with cancer; MGF was found overexpressed in human prostate cancer tissue, and in cell experiments the peptide increased the growth of prostate cancer cells [13]D.

Evidence against and what is unknown

Key cell findings on MGF could not be repeated in independent experiments, and the peptide sold online has not been found in the body [1] [7]D.

Evidence against

• A repeat experiment found no effect. Researchers at two drug companies tested the MGF peptide at up to 500 ng/ml. It did not increase the division of mouse muscle cells, human muscle precursor cells or mouse muscle stem cells, did not block maturation and did not activate signalling pathways in heart muscle cells. According to the researchers, the result calls into question whether MGF has any role in the body [7]D.
• The peptide has not been found in the body. According to a review, no product matching the MGF peptide has been isolated from cells, tissues or body fluids [1].
• The exercise effect did not repeat. In a randomised study heavy exercise did not raise muscle MGF in young men [5]A, although in an earlier study it rose in young people [2]B.
• Results in older people conflict. Strength exercise did not raise MGF in older people [2]B, but braking-type cycling did [3]B.

What the evidence does not support

• "MGF builds muscle": there is no human study of this, and even the cell results conflict [7, 8]D.
• "Injected MGF works like the muscle's own MGF": in humans only the muscle's own messenger RNA has been measured, not the effect of an injected peptide [1].
• "PEG-MGF is a studied, long-acting MGF": there are no peer-reviewed human studies of PEG-MGF, and no half-life has been reported [17].
• "The vial contains human MGF": modified versions have been found in products [14, 15]D.

What is unknown

It is not known whether injected MGF or PEG-MGF is absorbed, whether it reaches muscle, how long it stays in the body and whether it has any effect in humans. There are no data on long-term use or on the effects of stopping.

MGF dosage in studies

MGF has no approved dosage, and there is no dose studied in humans, because MGF has not been given to humans in studies [17]. The figures below are concentrations from cell experiments and amounts from animal experiments, not recommendations.

What the numbers do not tell you. A concentration in nanograms per millilitre or in nanomoles describes the substance in a test tube or tissue, not a dose in the body, and an animal amount is not converted into a human dose. Because there are no human studies, no safe or effective human dose is known. There are no doses studied in humans, so there is no dose page or calculator preset. Doses of other substances: Dosage.

MGF vs PEG-MGF vs IGF-1 LR3: what is the difference?

All three are related to IGF-1, but they are different substances, and there is no human study of any of them [17].

• MGF is a 24-amino-acid peptide matching the E part at the end of the IGF-1Ec form (IGF-1Eb in rodents) [1]. In the original cell experiments its effect seemed to run through a receptor other than the IGF-1 receptor [6]D.
• PEG-MGF is the same peptide with PEG attached. According to a review, attaching PEG changes how the substance moves and reaches tissues, so findings with MGF cannot be assumed to apply to PEG-MGF [17].
• "Full-length MGF" is a black-market product in which the Cologne laboratory found a modified protein resembling IGF-1Ec [15]D.
• IGF-1 LR3 is a modified form of mature IGF-1 that acts through the IGF-1 receptor. The review places PEG-MGF and IGF-1 LR3 in the same weakest evidence tier, with no peer-reviewed human studies [17].

Combinations and blends

Combinations of MGF have not been studied in humans. According to a review, peptides of the growth hormone and IGF-1 axis are often used together with anabolic steroids and other substances [17]. Because there are no human studies of MGF, there are no research data on its combinations either.

MGF has also been found in products that were supposed to contain follistatin [16]D, so a product can be an unintended blend. Blends in general: Peptide blends: what is in the vial and why the seller's declaration is not enough.

Another substance sold online and linked to muscle growth is follistatin (FS-344).

Is MGF legal in Finland?

MGF has no marketing authorisation and may not be sold or marketed as a medicine. It is in Annex 1 A of Fimea's medicines list, so in Finland it is controlled as a medicine and always treated like a prescription-only medicine [18]regulator.

• Medicines list. Annex 1 A of Fimea's decision 230/2025 names "MGF (mekaaninen kasvutekijä)". Substances in Annex 1 A are always treated, by their effect, like medicines supplied only on prescription [18]regulator.
• Marketing authorisation. On 14 Oct 2026 the EMA medicine data contained no medicine with MGF [21]regulator. According to doping researchers, MGF has not been approved for therapeutic use [14]D.
• Fimea's warning. Fimea has specifically warned against using injectable peptides bought online [20]regulator.
• The label "research use only" says what the product is meant for. It is not a permit for human use.

Overview of the law: Peptides and the law in Finland. Bringing them back from travel: Travelling with peptides.

This is not legal advice. Disclaimer.

Is MGF doping?

Yes. Class S2.3 of the WADA 2026 Prohibited List (growth factors and growth factor modulators) names mechano growth factors (MGFs). Class S2 is prohibited at all times, in and out of competition [19]regulator. According to the Cologne doping laboratory, MGF has been prohibited since 2005 [15]D.

Tests have been developed. A Belgian laboratory identified a modified MGF in two black-market preparations and found a way to tell it apart from the body's own form [14]D. In Cologne "full-length MGF" was added to doping tests, and it was detectable at 0.25 ng/ml [15]D.

Competitive athletes should check the current status with their national anti-doping agency, because the list is updated every year.

Product quality: how to assess an MGF product

The contents of MGF products are a documented problem. Two black-market preparations contained an MGF analogue whose end had been modified (C-terminal amidation), so it was not like human MGF [14]D.

A product sold as "full-length MGF" contained a protein resembling IGF-1Ec that lacked the last amino acid and had one amino acid swapped [15]D. MGF has been found in products labelled as follistatin [16]D.

On a certificate of analysis (COA), check whether the molecule was identified by mass spectrometry: doping laboratories told the modified versions apart precisely by their mass [14, 15]D. An HPLC purity figure alone does not show whether the substance is the right one. A guide: How to read a COA.

FAQ

Read the research yourself: sources

Every source opens the original publication or the regulator's page. The level shows what the source itself reports.

1. Matheny RW Jr, 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(3):865-875. PMID 20130113 (review)
2. Hameed M, Orrell RW, Cobbold M, Goldspink G, Harridge SD. Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. J Physiol. 2003;547(Pt 1):247-254. PMID 12562960 B
3. Hameed M, Toft AD, Pedersen BK, Harridge SD, Goldspink G. Effects of eccentric cycling exercise on IGF-I splice variant expression in the muscles of young and elderly people. Scand J Med Sci Sports. 2008;18(4):447-452. PMID 18067523 B
4. Greig CA, Hameed M, Young A, Goldspink G, Noble B. Skeletal muscle IGF-I isoform expression in healthy women after isometric exercise. Growth Horm IGF Res. 2006;16(5-6):373-376. PMID 17107821 B
5. Aperghis M, Velloso CP, Hameed M, et al. Serum IGF-I levels and IGF-I gene splicing in muscle of healthy young males receiving rhGH. Growth Horm IGF Res. 2009;19(1):61-67. PMID 18799338 A
6. Yang SY, Goldspink G. Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Lett. 2002;522(1-3):156-160. Erratum: FEBS Lett. 2006;580(10):2530. PMID 12095637 D
7. Fornaro M, Hinken AC, Needle S, 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 D
8. Kandalla PK, Goldspink G, Butler-Browne G, Mouly V. 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 D
9. Riddoch-Contreras J, Yang SY, Dick JR, Goldspink G, Orrell RW, Greensmith L. 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 C
10. Zhang B, Luo Q, Kuang D, Ju Y, Song G. Mechano-growth factor E peptide promotes healing of rat injured tendon. Biotechnol Lett. 2016;38(10):1817-1825. PMID 27334712 C
11. Carpenter V, Matthews K, Devlin G, et al. Mechano-growth factor reduces loss of cardiac function in acute myocardial infarction. Heart Lung Circ. 2008;17(1):33-39. PMID 17581790 C
12. Mavrommatis E, Shioura KM, Los T, Goldspink PH. The E-domain region of mechano-growth factor inhibits cellular apoptosis and preserves cardiac function during myocardial infarction. Mol Cell Biochem. 2013;381(1-2):69-83. PMID 23712705 C
13. Armakolas A, Philippou A, Panteleakou Z, et al. Preferential expression of IGF-1Ec (MGF) transcript in cancerous tissues of human prostate: evidence for a novel and autonomous growth factor activity of MGF E peptide in human prostate cancer cells. Prostate. 2010;70(11):1233-1242. PMID 20564425 D
14. Esposito S, Deventer K, Van Eenoo P. Characterization and identification of a C-terminal amidated mechano growth factor (MGF) analogue in black market products. Rapid Commun Mass Spectrom. 2012;26(6):686-692. PMID 22328223 D
15. Thevis M, Thomas A, Geyer H, Schänzer W. Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls. Growth Horm IGF Res. 2014;24(6):276-280. PMID 25466910 D
16. Reichel C, Gmeiner G, Thevis M. Detection of black market follistatin 344. Drug Test Anal. 2019;11(11-12):1675-1697. PMID 31758732 D
17. Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. PMID 42395176 (review)
18. Finland. Lääkeluettelo (Fimea medicines list), 230/2025, section 2 and annex 1 A ("MGF (mekaaninen kasvutekijä)"). Finlex regulator
19. World Anti-Doping Agency. 2026 Prohibited List, section S2.3 Growth factors and growth factor modulators: "Mechano growth factors (MGFs)" and "Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues". WADA regulator
20. Fimea. Fimea warns: do not use injectable peptides purchased online (29 Jun 2026). Fimea regulator
21. European Medicines Agency. Medicine data (data set of 14 Oct 2026): no product with mechano growth factor (MGF). EMA regulator

Sources read on 15 Oct 2026: PubMed abstracts (the Dominikowski review in full), Fimea decision 230/2025 and the EMA medicine data. The WADA 2026 Prohibited List was read from the PDF published by WADA.

Evidence levels: A = randomised human trial or meta-analysis · B = observational human study or case series · C = animal study · D = cell or laboratory study · E = not peer-reviewed · regulator = a regulator's assessment or decision, not research evidence. The marker official means official product information (summary of product characteristics or label); it is not research evidence. For a review, the level shows what kind of research the statement rests on. No level: statements that something has not been studied, reviews' interpretations, named hypotheses and the general rules in our certificate-of-analysis guide.

Content is general information about research, not medical advice. If you have symptoms, contact a healthcare professional.