Mechano growth factor (IGF-1Ec E-peptide)
MGF, mechano growth factor, IGF-1Ec, IGF-1 Ec peptide, MGF E-peptide, IGF-1Eb (rodent orthologue), MGF R23H (modified analogue found in confiscated products)
Mechano growth factor is not a separate hormone. It is a short peptide tail produced when the IGF-1 gene is spliced a particular way in mechanically loaded muscle, and the material sold as MGF is a synthetic copy of the final 24 amino acids of that tail. The splice variant itself is real and reproducibly detected in exercised muscle. The claim that injecting the isolated 24-mer does anything useful in a human being rests on no human evidence at all.
Mechanism
The human IGF1 gene produces several transcripts through alternative splicing at its 3' end. All encode the identical 70-residue mature IGF-1 peptide; they differ in the C-terminal extension, or E-domain, which is cleaved off during processing. The IGF-1Ea transcript predominates in liver. IGF-1Ec, first described by Yang, Goldspink and colleagues in stretched rabbit muscle in 1996 and later nicknamed mechano growth factor, arises from an insertion that shifts the reading frame and generates a distinct C-terminal sequence. The peptide sold as MGF is the final 24 residues of that extension, produced synthetically and administered on its own, something that never happens physiologically, where the E-peptide is part of a pro-IGF-1 molecule.
What the isolated E-peptide actually does is the crux, and the honest answer is that it is contested. Early work reported that MGF E-peptide activated muscle satellite cells and promoted proliferation without differentiation, and that it did so without binding IGF-1R, implying a distinct, unidentified receptor. That claim drove most of the commercial interest. It has not held up cleanly. Brisson and Barton showed in 2012 that E-peptide activity is dependent on the IGF-1 receptor, and Matheny's 2010 critical review in Endocrinology laid out how much of the MGF literature rests on synthetic peptide at concentrations far above anything the tissue would generate, on incomplete controls, and on an assumption that the E-peptide is liberated and acts as a free ligand, which has never been demonstrated in vivo in humans.
A further layer of complication: work from Barton's group indicates that the E-peptides matter chiefly as part of pro-IGF-1, influencing processing, secretion, local retention and receptor activation kinetics of the IGF-1 molecule they are attached to, rather than acting as standalone growth factors. On that reading, a free synthetic 24-mer is not a smaller version of MGF's function; it is a fragment removed from the context that gives it meaning.
What the research shows
The observational human data are solid and are frequently misrepresented. IGF-1Ec messenger RNA rises in skeletal muscle after high-resistance exercise and after mechanical damage, and the response is blunted in older muscle. McKoy and colleagues demonstrated the stretch- and stimulation-dependence of the splice variant in rabbit muscle in 1999. This establishes a genuine phenomenon: mechanical loading changes how the IGF-1 gene is spliced. It establishes nothing whatsoever about what happens when you inject the isolated E-peptide, because none of these studies administered anything.
The administration literature is entirely preclinical and internally inconsistent. Kandalla and colleagues reported in 2011 that synthetic MGF-E activated human muscle progenitor cells in culture, including cells from elderly donors, and increased their fusion potential. Various rodent studies report satellite cell activation and protective effects after cardiac or neural injury. Against that, Matheny's 2010 review documented the field's methodological weaknesses in detail, and Brisson and Barton's 2012 work directly undercut the central marketing claim by showing E-peptide activity requires IGF-1R. Barton's viral-expression studies in muscle indicate the E-peptides act by modifying IGF-1 processing and local retention rather than as independent ligands. Well over a decade on, no receptor for free MGF has been identified.
On human administration: ClinicalTrials.gov returns no interventional trial of MGF. PubMed returns no human administration study. The compound's presence in the human-facing scientific record is analytical. Thevis and colleagues characterised biotechnologically produced full-length MGF by mass spectrometry for doping-control purposes in 2014, and Cox and colleagues in 2017 analysed confiscated vials containing MGF R23H, a variant carrying an arginine-to-histidine substitution at position 23 that increases resistance to proteolysis. In other words, the only reason MGF appears in the human literature at all is that anti-doping laboratories have had to learn to detect it in seized products and biological samples.
Evidence assessment
Preclinical only
All administration data are cell-culture and animal; the human-facing literature is confined to observation of endogenous IGF-1Ec transcript expression and to anti-doping analytical characterisation, and no registered trial has ever administered MGF peptide to people.
Tiers are applied consistently across the library and re-checked when new trials read out. Read the grading method.
Key studies
Cloning and characterization of an IGF-1 isoform expressed in skeletal muscle subjected to stretch Preclinical only
Identified the alternatively spliced IGF-1 transcript induced by mechanical loading that was subsequently named mechano growth factor.
Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation Preclinical only
Mechanical loading and stimulation selectively induced the MGF splice variant relative to the systemic IGF-1Ea transcript.
Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration Preclinical only
Concluded that evidence for MGF acting as an independent growth factor is weak, that supraphysiological synthetic peptide concentrations dominate the literature, and that no MGF-specific receptor has been identified.
Insulin-like growth factor-I E-peptide activity is dependent on the IGF-I receptor Preclinical only
E-peptide effects required a functional IGF-1 receptor, contradicting the claim that MGF signals through a distinct IGF-1R-independent receptor.
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 Preclinical only
Synthetic MGF E-peptide increased proliferation and fusion potential of human muscle progenitor cells in culture, including cells from elderly donors.
Mass spectrometric characterization of a biotechnologically produced full-length mechano growth factor (MGF) relevant for doping controls Limited evidence
Established the analytical signature of biotechnologically produced MGF for anti-doping detection.
Detection and in vitro metabolism of the confiscated peptides BPC 157 and MGF R23H Limited evidence
Confiscated vials contained MGF R23H, a sequence-modified MGF analogue carrying an arginine-to-histidine substitution that increases resistance to proteolysis; detection methods were validated for anti-doping use.
Safety
There is no human safety data of any kind for administered MGF. Not limited data, not preliminary data, none. No trial has established a dose range, an adverse-event profile, an immunogenicity profile or an interaction profile in humans.
The theoretical risk profile is different from IGF-1's, and in some ways less clear precisely because the mechanism is unresolved. If the peptide acts through IGF-1R, as Brisson and Barton's data suggest, it inherits the mitogenic concerns that attach to IGF-1R agonism generally, albeit at what is likely to be much lower potency. If it acts through an unidentified receptor, as some of the older literature claims, then by definition nobody knows what else that receptor does. Neither scenario is reassuring.
Two concrete concerns are worth stating. First, immunogenicity: a synthetic basic 24-mer injected repeatedly is a plausible immunogen, and antibodies raised against the E-peptide could in principle cross-react with endogenous pro-IGF-1. No study has looked. Second, product identity: the confiscated material analysed by Cox and colleagues was not MGF at all but MGF R23H, a sequence-modified analogue with even less biological characterisation than the parent peptide. Anyone buying 'MGF' online has no reliable way of knowing which of these they have received, or whether the vial contains a correctly synthesised peptide of any kind.
Regulatory status
| Jurisdiction | Status |
|---|---|
| United Kingdom | No MHRA marketing authorisation and no clinical trial authorisation. Supply for human use without a marketing authorisation breaches the Human Medicines Regulations 2012. Not controlled under the Misuse of Drugs Act 1971. The MHRA has taken enforcement action against sellers of unlicensed injectable products marketed to gym and bodybuilding audiences. |
| United States | Not approved by FDA for any indication and never the subject of a clinical development programme. Not a dietary supplement; marketing it for human use renders it an unapproved new drug and misbranded under the Federal Food, Drug, and Cosmetic Act. Sold exclusively through research-chemical channels under a 'for research use only' label. Not DEA-scheduled. |
| WADA (sport) | Prohibited at all times. The WADA Prohibited List, section S2.3 (Growth Factors and Growth Factor Modulators), explicitly names 'Mechano Growth Factors (MGFs)'. Class S2 substances are non-Specified Substances. Validated mass-spectrometry methods exist for MGF (Thevis et al., 2014) and for the R23H analogue found in confiscated products (Cox et al., 2017), and in vitro metabolite work indicates both should remain detectable in biological samples. |
Questions
No, though they come from the same gene. IGF-1Ec, the splice variant nicknamed mechano growth factor, encodes the identical mature IGF-1 peptide attached to a different C-terminal extension called the Ec E-domain. The product sold as 'MGF' is not IGF-1 at all; it is a synthetic copy of just the last 24 residues of that extension, without the IGF-1 portion. In the body the E-peptide is never released as a free 24-mer in the way the injected product presents it.
That was the original claim and it is the basis of most MGF marketing, but the evidence has moved against it. Brisson and Barton demonstrated in 2012 that E-peptide activity depends on a functional IGF-1 receptor, and no distinct MGF receptor has ever been identified despite decades of searching. Matheny's 2010 review in Endocrinology set out the methodological reasons to treat the IGF-1R-independent claim sceptically.
None. ClinicalTrials.gov lists no interventional trial of MGF and PubMed contains no human administration study. The human data that exist are observational studies of endogenous IGF-1Ec transcript levels rising in muscle after resistance exercise, which say nothing about the effect of injecting a synthetic peptide fragment, plus anti-doping analyses of confiscated vials.
A modified version of the MGF peptide in which the arginine at position 23 is replaced by histidine, introduced to slow enzymatic breakdown of a peptide that is otherwise degraded very quickly. It appears in black-market products rather than in the biological literature: Cox and colleagues identified it in confiscated vials in 2017. It is a novel sequence with even less biological characterisation than MGF itself, and buyers generally have no way of knowing whether they have received it.