Peptides & growth hormone

MGF

Updated · 23 sources · Editorial policy

Mechano growth factor (MGF) is the name given to a splice variant of the insulin-like growth factor 1 (IGF-1) gene that muscle switches on after stretch, heavy loading or damage. In humans this variant is called IGF-1Ec; in rodents it is IGF-1Eb. The same name is also used for a short synthetic peptide copied from the tail end of that variant, and this peptide is what is sold online as “MGF.”

MGF has never been approved as a medicine, and no controlled human trials of injected MGF have been published. Most of what is known comes from muscle biopsies after exercise, cell culture and animal studies. Those results conflict: an independent replication by two pharmaceutical companies found that the synthetic peptide had no effect on muscle stem cells. MGF has been banned in sport by the World Anti-Doping Agency (WADA) since 2005.

This page summarizes what the laboratory, animal and exercise studies and the anti-doping literature report. It is for education only and is not medical advice.

Property Detail
Class Peptide derived from a splice variant of the IGF-1 gene (IGF-1Ec in humans, IGF-1Eb in rodents)
What “MGF” products contain Usually a synthetic peptide matching the last 24 amino acids of the human Ec E-domain; modified and full-length versions also circulate
Approval Not approved for therapeutic use
Human trials None published for injected MGF
Half-life Not established; no human pharmacokinetic data
Key mechanism fact Proposed to act separately from the IGF-1 receptor; the synthetic peptide did not activate the IGF-1 receptor in a 2016 assay
Evidence status Cell and animal studies only, with a failed independent replication in muscle cells
WADA status Prohibited at all times (S2.3, “mechano growth factors”)

What it is

The IGF-1 gene can be spliced in several ways. Every version produces the same mature 70-amino-acid IGF-1 hormone (see IGF-1), but each carries a different tail, called the E-domain, that is normally cut off (Matheny et al., Endocrinology 2010):

  • IGF-1Ea is the main form, made by the liver and most tissues.
  • IGF-1Ec (human) / IGF-1Eb (rodent) includes an extra stretch of genetic code from exon 5. This insert shifts the reading frame, so the tail has a different amino-acid sequence. This is the variant that was named MGF.

Geoffrey Goldspink’s group in London first cloned the variant in 1996 from rabbit muscle forced to grow by active stretch. It was readily detected in stretched or exercised muscle, but very little was found in resting muscle (Yang et al., J Muscle Res Cell Motil 1996). The insert is 49 base pairs long in humans and 52 in rodents (Kandalla et al., Mech Ageing Dev 2011).

One name, several different things

Reviewers have pointed out that “MGF” is used for three things that are not the same (Matheny et al., Endocrinology 2010): the mRNA splice variant, the E-peptide that the variant actually encodes, and a synthetic peptide matching the last 24 amino acids of that E-peptide (25 in rodents). Products sold as MGF add more variations.

Form What it is Where the evidence comes from
IGF-1Ec / IGF-1Eb mRNA The splice variant itself, measured in tissue Human muscle biopsies; animal tissue
Ec / Eb E-peptide The tail the variant encodes, cut from the precursor protein Detected in human and rodent tissues in 2017
Synthetic MGF peptide Lab-made copy of the last 24 amino acids of the human Ec tail Cell and animal studies
Black-market MGF analogues Synthetic MGF with a modified end (amidated) or a single amino-acid substitution Anti-doping lab analyses of seized products
“Full-length MGF” A roughly 12.3 kDa protein closely related to IGF-1Ec, including the IGF-1 portion Anti-doping lab analysis (2014); receptor assays
PEG-MGF MGF peptide attached to polyethylene glycol (PEG), marketed as longer-acting No human studies; covered on its own page

These forms should not be treated as interchangeable. Full-length MGF contains the IGF-1 hormone and acts on the IGF-1 receptor; the short synthetic peptide does not (Janssen et al., PLoS One 2016).

How it works in the body

The proposed role

The original theory, sometimes called the “MGF hypothesis,” runs as follows (Hill & Goldspink, J Physiol 2003):

  • After muscle damage, the MGF variant is switched on quickly and then falls within a few days (shown in rats).
  • This early pulse is thought to activate satellite cells, the muscle stem cells that divide and fuse with damaged fibers.
  • Later, splicing shifts toward IGF-1Ea, which supplies mature IGF-1 to drive the protein synthesis needed to finish the repair.

Early cell work supported a separate role for the tail. In mouse muscle cells, the synthetic E-domain peptide increased proliferation and held back differentiation into mature fibers, and blocking the IGF-1 receptor did not stop this effect (Yang & Goldspink, FEBS Lett 2002).

Doubts about whether the peptide exists naturally

A 2010 review in Endocrinology questioned the theory on several grounds (Matheny et al., Endocrinology 2010):

  • No 24-amino-acid peptide matching synthetic MGF had been isolated from cells, tissues or body fluids.
  • No known enzyme cuts the precursor at the point needed to release such a peptide.
  • In muscle, levels of the MGF mRNA have never been shown to exceed, or even approach, levels of the main IGF-1Ea mRNA, even during early repair.

Later work showed that the longer Ec E-peptide is produced in human and rodent tissues, including muscle, liver and heart. It is made together with its precursor protein, and its levels changed during muscle regeneration after damaging exercise in humans (Vassilakos et al., Growth Horm IGF Res 2017). That supports a natural E-peptide, but not the specific 24-amino-acid peptide that is sold.

Pharmacokinetics

No study has measured the absorption, half-life or elimination of any MGF peptide in humans. Half-life figures quoted online could not be traced to a primary source. In a test-tube study using human plasma, an MGF variant seized by authorities (one with a single amino-acid substitution) showed “good stability,” and the authors expected it to be detectable in urine (Cox et al., Drug Test Anal 2017). That is not a human half-life, and it applies only to that variant.

Regulatory status

MGF has not been approved for therapeutic use (Esposito et al., Rapid Commun Mass Spectrom 2012). There is no prescription product, labeled dose or approved route of administration. A 2026 clinical review of growth-hormone and IGF-1-axis peptides placed PEG-MGF in its lowest evidence tier, meaning no peer-reviewed human studies exist (Dominikowski et al., Front Endocrinol 2026).

What the research shows

MGF expression after exercise in humans

The most solid human data are muscle biopsies measuring the body’s own MGF mRNA. They show that loading and muscle damage switch the variant on, and that the response may be weaker in older people:

Study Participants Stimulus Finding
Hameed et al., J Physiol 2003 8 young (25–36 y), 7 older (70–82 y) 10 sets of 6 single-leg knee extensions at 80% of 1RM; biopsy 2.5 h later MGF mRNA rose in the young but not the older group; IGF-1Ea unchanged. At rest, MGF mRNA was ≈ 100-fold lower than IGF-1Ea
Hameed et al., J Physiol 2004 Older men, mean age 74 Resistance training, GH injections, or both 5 weeks of training: MGF mRNA +163%; training plus GH: +456%; GH alone: no change at 5 weeks, +80% at 12 weeks
Hameed et al., Scand J Med Sci Sports 2008 9 young (20–27 y), 8 older (67–75 y) 60 min of eccentric (reverse-pedal) cycling MGF mRNA rose in both age groups; IGF-1Ea unchanged
Vassilakos et al., Growth Horm IGF Res 2017 Human muscle after damaging exercise Exercise-induced muscle damage The Ec E-peptide itself was detected and changed during regeneration

These studies show that the variant responds to exercise. They do not show that adding synthetic MGF from outside the body builds muscle. In rats, the older animals’ poorer response to overload was linked to much lower MGF expression (Owino et al., FEBS Lett 2001), which is why MGF has been discussed as a target in age-related muscle loss.

Cell studies: conflicting results

Study Model Result
Yang & Goldspink, FEBS Lett 2002 Mouse myoblast cell line Synthetic E-domain peptide increased proliferation and inhibited differentiation, independent of the IGF-1 receptor
Kandalla et al., Mech Ageing Dev 2011 Human muscle stem cells from donors of different ages Peptide extended the cells’ proliferative lifespan in cells from newborn and young adult donors, but not from older adults
Fornaro et al., Am J Physiol Endocrinol Metab 2014 Mouse and human myoblasts, primary mouse muscle stem cells, cardiac cells MGF peptide up to 500 ng/mL did not increase proliferation or block differentiation; neither native nor stabilized peptide activated cardiac-cell signaling. Mature IGF-1 and full-length IGF-1Eb did increase proliferation
Janssen et al., PLoS One 2016 Cell-based receptor activation assays Synthetic human MGF and a stabilized analogue did not activate the IGF-1 or insulin receptors; full-length MGF did

The 2014 study is the most important negative result. It was run at two pharmaceutical companies, including Novartis, specifically to reproduce the earlier claims, and the authors concluded that the findings “call in to question” a physiological role for MGF (Fornaro et al., 2014).

In the 2016 receptor study, full-length MGF reached a similar maximum activation of the IGF-1 receptor as IGF-1 at high concentrations, but needed a much higher concentration to do so: EC50 (the concentration giving half the maximal effect) 7.83 nmol/L (95% CI 4.87–12.58) vs 0.86 nmol/L (95% CI 0.69–1.07) for IGF-1. This means full-length MGF behaves more like a weaker IGF-1 than like the short peptide.

Animal studies

Several animal studies, mostly from groups involved in developing the MGF concept, have reported protective effects. All were in animals, and none has been followed by a human trial:

  • Heart attack in sheep. After experimentally induced infarcts, sheep given the MGF E-domain peptide had 35% less compromised heart muscle than controls and better-preserved cardiac function after 8 days (Carpenter et al., Heart Lung Circ 2008).
  • Heart attack in mice. A synthetic E-domain peptide analogue given at the time of infarction preserved cardiac contractility and reduced cell death at 2 weeks (Mavrommatis et al., Mol Cell Biochem 2013).
  • Stroke model in gerbils. The synthetic peptide protected vulnerable brain neurons after temporary loss of blood flow, through a route independent of the IGF-1 receptor (Dluzniewska et al., FASEB J 2005).
  • ALS model in mice. Gene delivery of MGF into leg muscles (not peptide injection) improved muscle strength and motor neuron survival, with more neurons surviving than after IGF-1 gene delivery (Riddoch-Contreras et al., Exp Neurol 2009).

These studies used research-grade peptides or gene vectors given under controlled conditions, often directly into the target tissue. They do not establish that injected MGF builds muscle or speeds recovery in people.

Human trials

No randomized or controlled human trial of MGF, in any form, has been published. A 2026 review of performance-enhancing peptides concluded that claims of faster recovery or better body composition with PEG-MGF “remain unproven” (Dominikowski et al., Front Endocrinol 2026).

Side effects and risks

No human safety data

Because no human trials exist, there is no measured rate of any side effect, no known safe dose and no data on interactions. The 2026 review lists the adverse effects reported with this class of unregulated growth-hormone and IGF-1-axis peptides, while noting there are no human data for PEG-MGF specifically (Dominikowski et al., 2026):

  • low or high blood sugar;
  • fluid retention;
  • muscle and joint pain;
  • injection-site reactions.

The MGF variant has been studied in cancer tissue. All of the evidence is laboratory or tissue-based, and none shows that MGF products cause cancer:

  • MGF was expressed much more strongly in prostate cancer and precancerous prostate tissue than in normal prostate. In prostate cancer cell lines, the synthetic E peptide stimulated growth through a route that did not depend on the IGF-1 or insulin receptors (Armakolas et al., Prostate 2010).
  • In 83 prostate cancer surgical specimens, higher IGF-1Ec levels were linked to more advanced stage (p = 0.004) and, weakly, to higher Gleason score (r = 0.247) (Savvani et al., Anticancer Res 2013).
  • Full-length MGF products activate the IGF-1 receptor (Janssen et al., 2016). The approved IGF-1 drug carries a labeled cancer warning; see IGF-1.

What is actually in the vial

Anti-doping laboratories have analyzed products sold as MGF and found forms that differ from the peptide used in research:

  • Two black-market products contained an MGF analogue with a chemically modified (amidated) end (Esposito et al., 2012).
  • Seized vials contained an MGF variant with one amino-acid substitution (Cox et al., 2017).
  • A product marketed as “full-length MGF” was a 12,264.9 Da protein closely related to IGF-1Ec, with a missing end residue and one substitution (Thevis et al., Growth Horm IGF Res 2014).

These products are made outside any regulated supply chain, so identity, dose, purity and sterility are not controlled. The results of research on one form cannot be assumed to apply to another.

MGF has been prohibited by WADA since 2005 (Thevis et al., 2014). The WADA 2026 Prohibited List names “mechano growth factors (MGFs)” under S2.3, growth factors and growth factor modulators, banned both in and out of competition. The same section bans IGF-1 and its analogues, such as IGF-1 LR3 and IGF-1 DES.

Detection methods have been published. Full-length MGF was detectable at 0.25 ng/mL using adapted routine doping tests (Thevis et al., 2014), and one lab described a potentially diagnostic mass-spectrometry marker that separates the amidated analogue from the natural form (Esposito et al., 2012).

Key takeaways

  • A splice variant, not a drug. MGF is the IGF-1Ec (human) / IGF-1Eb (rodent) variant of the IGF-1 gene. What is sold is usually a synthetic copy of the last 24 amino acids of its tail, or a modified version of it.
  • Exercise turns it on. Muscle biopsies show MGF mRNA rises after heavy or damaging exercise, with a weaker response in older adults in some studies.
  • The synthetic peptide’s effects are disputed. Early cell studies reported effects on muscle stem cells, but a 2014 industry replication found none, and the peptide did not activate the IGF-1 receptor.
  • No human trials. All evidence for benefit comes from cell and animal studies; there are no human data on dosing, half-life or safety.
  • Product contents vary. Anti-doping labs have found amidated, substituted and full-length MGF forms in black-market products.
  • Banned in sport. WADA has prohibited MGFs at all times since 2005, and detection methods exist.

Sources

  1. Yang S, Alnaqeeb M, Simpson H, Goldspink G. Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch. J Muscle Res Cell Motil. 1996;17(4):487–495. PubMed.
  2. 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. PubMed.
  3. 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(Pt 2):409–418. PubMed.
  4. 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. PubMed.
  5. Vassilakos G, Philippou A, Koutsilieris M. Identification of the IGF-1 processing product human Ec/rodent Eb peptide in various tissues: evidence for its differential regulation after exercise-induced muscle damage in humans. Growth Horm IGF Res. 2017;32:22–28. PubMed.
  6. 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. PubMed.
  7. Hameed M, Lange KH, Andersen JL, et al. The effect of recombinant human growth hormone and resistance training on IGF-I mRNA expression in the muscles of elderly men. J Physiol. 2004;555(Pt 1):231–240. PubMed.
  8. 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. PubMed.
  9. Owino V, Yang SY, Goldspink G. Age-related loss of skeletal muscle function and the inability to express the autocrine form of insulin-like growth factor-1 (MGF) in response to mechanical overload. FEBS Lett. 2001;505(2):259–263. PubMed.
  10. 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. PubMed.
  11. 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. PubMed.
  12. Janssen JA, Hofland LJ, Strasburger CJ, van den Dungen ES, Thevis M. 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. PubMed.
  13. 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. PubMed.
  14. 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. PubMed.
  15. Dluzniewska J, Sarnowska A, Beresewicz M, 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. PubMed.
  16. Riddoch-Contreras J, Yang SY, Dick JR, 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. PubMed.
  17. 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. PubMed.
  18. Savvani A, Petraki C, Msaouel P, et al. IGF-IEc expression is associated with advanced clinical and pathological stage of prostate cancer. Anticancer Res. 2013;33(6):2441–2445. PubMed.
  19. 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. PubMed.
  20. Cox HD, Miller GD, Eichner D. Detection and in vitro metabolism of the confiscated peptides BPC 157 and MGF R23H. Drug Test Anal. 2017;9(10):1490–1498. PubMed.
  21. 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. PubMed.
  22. 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. PubMed.
  23. World Anti-Doping Agency. 2026 Prohibited List. WADA 2026 Prohibited List.