MGF

What it actually is

In 1996 a group at the Royal Free in London found that rabbit muscle under stretch expresses a second IGF-1 messenger RNA, carrying a 52 base-pair insert that the liver form does not have. That variant was later nicknamed mechano growth factor, because it appeared in response to mechanical load.

What gets sold as MGF is not that protein. It is a synthetic 24-amino-acid peptide copied from the C-terminal E domain, the piece that is cleaved off the 70-amino-acid mature IGF-1. A 2010 review in Endocrinology made the awkward point plainly: no equivalent peptide has ever been isolated from cultured cells, their medium, or animal tissue or fluid.

How it’s thought to work

• Proliferation, not differentiation — In the 2002 cell work the E domain increased myoblast proliferation while holding off terminal differentiation, the opposite of what mature IGF-1 does.
• A receptor nobody has found — In that same work, blocking the IGF-1 receptor with an antibody did not stop the effect, which the authors read as a different receptor. That receptor has still not been identified.
• Satellite cell story — The proposed sequence is that the Eb/Ec variant goes up first after damage, alongside markers of satellite cell proliferation, with the IGF-1Ea form rising later as fibres mature.
• Receptor assays say nothing — A 2016 receptor-activation study found that human MGF and the stabilised Goldspink-MGF produced no IGF-1 receptor activation at all. Only the full-length protein did.

What the research says

The origin science holds up: the splice variant is real, it rises after high-resistance exercise in young human muscle, and the response is blunted in older subjects. The peptide is where it falls apart. In 2014 two pharmaceutical companies ran the key experiments again and published the result in Am J Physiol Endocrinol Metab: concentrations up to 500 ng/ml failed to increase proliferation of mouse C2C12 cells or primary human myoblasts, failed to delay differentiation, and failed to activate p-ERK in cardiac myocytes, while mature IGF-1 and full-length IGF-1Eb worked fine in the same dishes. Their closing line questions whether the MGF peptide has a physiological role at all. Set against that are animal studies from other labs: in sheep the E domain peptide preserved heart function after an induced infarct, and in gerbils it protected vulnerable neurons after brain ischaemia. Those are animal results, in injury models, with the peptide placed where it was wanted.

• 1996: a stretch-induced IGF-1 splice variant is cloned from rabbit muscle, and the human equivalent is detected after altered physical activity.
• 2003: high-resistance exercise raised the variant in young human muscle but not in elderly muscle, which is the age-related interest in it.
• 2014: two pharmaceutical companies found no effect of the synthetic 24-mer on human or mouse myoblasts at up to 500 ng/ml.
• 2016: human MGF and the stabilised analogue produced no measurable IGF-1 receptor activation in a kinase receptor activation assay.
• Zero human trials of the peptide. ClinicalTrials.gov lists no study of it, and the only human-sample work is doping-control chemistry built to detect it.

Reported protocols

These are the doses the peptide community actually reports running (Reddit & forums), alongside published research — logged for education, not as a recommendation to use.

Common use cases

Mixing it (reconstitution)

Freeze-dried peptides must be reconstituted with bacteriostatic water before they can be measured. Carl’s calculator turns “mg in the vial + ml of water + target dose” into “units on the syringe” — and tells you how long the vial lasts.

→ Open the Reconstitution Calculator

Injection & handling

There is no administration guide on this page and that is deliberate, not an oversight. An injection protocol implies someone established a dose, a schedule and a safety margin, and for MGF nobody has. Three things worth holding on to instead. First, the replication failure is the single most important fact about this compound and it gets left out of almost every page selling it. Second, the E peptide has been reported as mitogenic in human prostate cancer cells, through a route independent of the IGF-1 receptor, which is a reason for caution rather than a reason to experiment. Third, if the reason for looking at this is a real injury that will not heal, that is a job for a sports physician with imaging, not a vial of an unapproved peptide.

Stacks it appears in

• With IGF-1 LR3 — the pair is sold on a proliferate-then-grow theory. Neither has a human trial behind it, so the combination inherits two unknowns rather than resolving either.
• With GH secretagogues — ipamorelin and CJC-1295 appear beside it in the same online protocols. Stacking multiplies the uncertainty, and the 2026 review groups all of them together as evidence-poor.
• With BPC-157 or TB-500 — the standard injury stack. SAHPRA names both of those as examples of illegally marketed peptides, and TB-500 is named on the WADA list as well.

Sources

1. Yang S et al. 1996, J Muscle Res Cell Motil. Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch (PMID 8884603)
2. Yang SY, Goldspink G 2002, FEBS Lett. Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation (PMID 12095637)
3. Matheny RW et al. 2010, Endocrinology. Minireview: Mechano-growth factor, a putative product of IGF-I gene expression (PMID 20130113)
4. Fornaro M et al. 2014, Am J Physiol Endocrinol Metab. MGF peptide has no apparent effect on myoblasts or primary muscle stem cells (PMID 24253050)
5. Hameed M et al. 2003, J Physiol. Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise (PMID 12562960)
6. Janssen JA et al. 2016, PLoS One. Potency of full-length MGF to induce maximal activation of the IGF-I R (PMID 26991004)
7. Carpenter V et al. 2008, Heart Lung Circ. Mechano-growth factor reduces loss of cardiac function in acute myocardial infarction (PMID 17581790)
8. Dluzniewska J et al. 2005, FASEB J. Neuroprotective effect of the C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia (PMID 16144956)
9. Armakolas A et al. 2010, Prostate. Preferential expression of IGF-1Ec (MGF) in cancerous prostate tissue and growth activity of the MGF E peptide (PMID 20564425)
10. Thevis M et al. 2014, Growth Horm IGF Res. Mass spectrometric characterization of a biotechnologically produced full-length MGF relevant for doping controls (PMID 25466910)
11. Dominikowski A et al. 2026, Front Endocrinol. Performance-enhancing peptides modulating the GH-IGF1 axis (PMID 42395176)
12. WADA 2026 Prohibited List, S2.3 growth factors
13. SAHPRA, Peptide Products: Public Information (May 2026)
14. ClinicalTrials.gov search: mechano growth factor / MGF

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