MGF.
MGF is a splice variant of insulin-like growth factor 1 (IGF-1), designated IGF-1Ec in humans and IGF-1Eb in rodents, produced locally in skeletal muscle in response to mechanical loading or damage.
MGF is a splice variant of insulin-like growth factor 1 (IGF-1), designated IGF-1Ec in humans and IGF-1Eb in rodents, produced locally in skeletal muscle in response to mechanical loading or damage. MGF is research / preclinical, and PepCue grades its published evidence F tier (15/100). Also known as mechano growth factor · IGF-1Ec. This is a research reference, not medical or dosing advice.
What it is
MGF is a splice variant of insulin-like growth factor 1 (IGF-1), designated IGF-1Ec in humans and IGF-1Eb in rodents, produced locally in skeletal muscle in response to mechanical loading or damage. The synthetic 'MGF' peptide that is sold and studied is the unique C-terminal E-domain (Ec) portion, not the full IGF-1 molecule. It was characterized largely by Geoffrey Goldspink's group, who proposed it as an autocrine and paracrine signal that activates muscle satellite cells. It remains a preclinical research compound with no approved use.
How it works
The mechanistic hypothesis is that the MGF E-peptide, generated by a reading-frame shift in IGF-1 splicing after mechanical stress, activates satellite (muscle stem) cells to proliferate through a receptor thought to be distinct from the classical IGF-1 receptor. In this model MGF acts as a local kick-start for repair that precedes the mature IGF-1 which later drives differentiation. This mechanism is characterized in cell and animal models, and even there it is contested. Several independent laboratories have been unable to reproduce a direct proliferative effect of the isolated E-peptide.
Mechanism pathways
Downstream growth signalling through the IGF-1 receptor and its splice variants.
Insulin-like growth factor 1 is the main mediator of growth hormone's anabolic effects. Growth hormone binds its own receptor on hepatocytes, which dimerises and signals through the JAK2 and STAT5 pathway to drive IGF-1 transcription. Circulating IGF-1 then binds the IGF-1 receptor, a receptor tyrosine kinase closely related to the insulin receptor, which activates the PI3K, Akt, and mTOR cascade alongside the Ras and MAPK cascade. The result is increased protein synthesis, cell proliferation, and suppression of programmed cell death. Muscle also produces IGF-1 locally in response to mechanical loading, and this local supply is thought to matter more for tissue repair than the circulating pool does. A critical regulatory layer is the family of six IGF-binding proteins. The great majority of circulating IGF-1 is bound to these proteins rather than free, which limits how much reaches receptors at any moment and prevents excessive signalling. Several compounds in this group are engineered specifically to evade that control, using amino-acid substitutions and terminal extensions that drop binding-protein affinity dramatically. The consequence is a much larger free fraction and a far longer functional presence than native IGF-1, which is the intended effect and also the source of the main concern about them. A separate branch involves splice variants. Mechanical stress shifts IGF-1 splicing to produce a variant with a distinct carboxy-terminal E-domain, and the isolated E-peptide has been proposed to act on muscle satellite cells through a receptor different from the classical IGF-1 receptor, expanding the stem cell pool before mature IGF-1 drives differentiation. Attaching polyethylene glycol to this peptide is a stability modification rather than a change in mechanism. The honest position differs sharply between branches. Growth hormone and IGF-1 receptor biology is textbook physiology, well established in humans, and recombinant growth hormone is an approved medicine for defined deficiency states. The splice-variant branch is far weaker: independent laboratories have not consistently reproduced the proposed proliferative effect of the isolated E-peptide, and there are essentially no controlled human trials of it. Across the whole pathway, unregulated amplification of a proliferative growth signal raises theoretical concerns about promoting the growth of existing abnormal cells, and these compounds other than approved growth hormone have no established human safety record.
The evidence
Early work from Goldspink and colleagues in the late 1990s and 2000s reported that mechanically induced IGF-1Ec/MGF expression tracked with muscle hypertrophy and repair, and some cell studies suggested the E-peptide activated satellite cells. The foundational experiments were expression studies rather than treatment studies. Rabbit skeletal muscle subjected to stretch and electrical stimulation showed a shift in IGF-1 splicing toward the alternative variant (PMID 10087355), and rodent muscle subjected to local damage showed the same splicing shift alongside satellite cell activation (PMID 12692175). Those designs establish a correlation between a mechanical stimulus and a transcript, in small animal groups, over short time courses, without blinding and without any peptide being administered. They do not show that giving the isolated E-peptide does anything. That story is directly challenged by Fornaro et al. in the American Journal of Physiology-Endocrinology and Metabolism (2014, PMID 24253050), who found that the MGF E-peptide at concentrations up to 500 ng/mL had no apparent effect on the proliferation of C2C12 myoblasts or primary human muscle stem cells, whereas mature IGF-1 did. That paper tested synthetic E-peptide obtained from more than one source and included the positive control that much of the earlier literature lacked, which is why it carries substantial weight against the original claim. The contrast with better-characterized molecules in the same family is stark. Mature IGF-1 has decades of receptor pharmacology behind it, and its recombinant form mecasermin is an approved drug for severe primary IGF-1 deficiency, with defined pharmacokinetics, a known hypoglycemia risk, and labeled monitoring requirements. MGF has none of that. There are essentially no controlled human trials of synthetic MGF for muscle growth or repair, no human pharmacokinetic data, no confirmed receptor, no toxicology package, and no outcome data of any kind. The evidence base is preclinical, mixed, and negative in key experiments.
The evidence, in brief
The peptide sold as MGF is the C-terminal E-domain of the IGF-1Ec splice variant, not full IGF-1. Its satellite-cell story is contested rather than merely unproven: Fornaro and colleagues found the isolated E-peptide had no apparent effect on myoblast or human muscle stem cell proliferation, while mature IGF-1 did. There are no human trials of synthetic MGF, and it is research-use-only and WADA-prohibited.
- MGF E-peptide has no apparent effect on myoblasts or muscle stem cellsAm J Physiol Endocrinol Metab, 2014 (PMID 24253050)
- PubMed search: mechano growth factor IGF-1Ec musclePubMed / NCBI
Evidence maturity
An evidence-only reading: approval status, human vs preclinical data, mechanism and safety. Popularity never raises it. Research file #042
Little indexed evidence or largely speculative.
Mostly online reports, no real study base yet.
Claim receipts
Popular claims about MGF, checked against the state of the evidence. The verdict describes evidence maturity, never an invented study result.
An independent laboratory found no apparent effect of the isolated E-peptide on myoblasts or human muscle stem cells, while mature IGF-1 did act.
Expression studies link mechanical loading to the splice variant; administering the isolated peptide is a separate claim that did not replicate.
Mature IGF-1 has decades of receptor pharmacology and an approved recombinant drug; the E-peptide has no confirmed receptor.
No clinical trial exists, so there is no adverse-event profile, immunogenicity assessment or chronic toxicology.
Safety profile
There is no meaningful human safety data for injected synthetic MGF. No clinical trial has been conducted, so there is no reported adverse-event profile, no established tolerated exposure, no immunogenicity assessment, and no chronic toxicology. Theoretical concerns follow from IGF-1 biology, including unregulated growth-factor signaling and the possibility of promoting proliferation of pre-existing tumor cells, although the isolated E-peptide's own activity is uncertain. That uncertainty cuts both ways. A peptide that does not measurably act on muscle stem cells in culture is unlikely to carry the full risk profile of mature IGF-1, but it is also not established to be inert, and the receptor it supposedly acts through has never been identified, which makes off-target prediction impossible. Injected peptides carry generic risks independent of the sequence, including local reactions, sterile abscess, infection from non-sterile preparation, and antibody formation against a foreign or modified sequence. Pegylated versions sold as PEG-MGF add a further unknown, since polyethylene glycol conjugates raise tissue-accumulation and anti-PEG antibody questions that have not been examined for this molecule at all. Material sold online as MGF or PEG-MGF is unregulated and of unverified identity and purity, and independent testing of the grey peptide market has repeatedly found mislabeled contents, under-filled vials, and bacterial contamination. Any legitimate study would require sterility and endotoxin testing of the material, immunogenicity monitoring, measurement of the IGF-1 axis, and exclusion of participants with a cancer history before first exposure. Human safety is uncharacterized.
Compound notes
- MGF (mechano growth factor) is a splice variant of IGF-1, designated IGF-1Ec in humans and IGF-1Eb in rodents, expressed locally in skeletal muscle after mechanical loading or damage.
- The synthetic peptide sold as MGF is the unique C-terminal E-domain, not the full IGF-1 molecule.
- It was proposed by Geoffrey Goldspink's group as a local signal that activates muscle satellite cells ahead of mature IGF-1.
- Key experiments contradict that model: Fornaro et al. (2014) found the isolated E-peptide had no apparent effect on myoblasts or human muscle stem cells, whereas mature IGF-1 did.
MGF is the E-domain offcut of the IGF-1 gene, not the growth factor itself. In head-to-head cell work, mature IGF-1 drove proliferation and the isolated E-peptide did not.
- No meaningful human safety data; there are essentially no controlled human trials of synthetic MGF.
- Theoretical concerns follow from IGF-1 biology, including unregulated growth-factor signaling and possible proliferation of pre-existing tumor cells.
- Not approved anywhere; research-use-only and prohibited in sport by WADA.
Regulatory status
MGF is not approved by the FDA or any regulator and holds no marketing authorization for any indication. It is sold only as a research chemical. Growth-factor peptides of this type are prohibited in sport by WADA.
Sold research-use-only; human evidence is limited or preclinical.
By the numbers
- 01An IGF-1 splice variant (IGF-1Ec in humans, IGF-1Eb in rodents)
- 02Synthetic 'MGF' is the C-terminal E-domain peptide, not full IGF-1
- 03Proposed to activate muscle satellite cells after mechanical load or damage
- 04Named for mechanically induced expression; characterized by Goldspink's group
- 05Fornaro 2014 (PMID 24253050) found no effect of the isolated E-peptide
- 06No human trials; research-use-only and WADA-prohibited
MGF: research formats
Choose the format you are researching to see route-specific notes.
Synthetic MGF has never been evaluated in a human trial, so no human administration format exists.
MGF is the C-terminal E-domain peptide of the IGF-1Ec splice variant. Everything known about it comes from cell and animal experiments, and the key experiment (Fornaro 2014) found no effect of the isolated E-peptide on myoblasts or muscle stem cells. There are essentially no controlled human trials of synthetic MGF, so this page does not present a human administration format or any example concentration math.
Vendors sell MGF as a lyophilized vial labeled for laboratory use. That a product exists is not evidence that a human format has been studied: nothing in the literature establishes a route, a schedule, or a tolerated exposure in people.
MGF is not approved by any regulator, holds no marketing authorization, and growth-factor peptides of this type are prohibited in sport by WADA.
Sources
Every factual claim above resolves to a real, published source.
- MGF E-peptide has no apparent effect on myoblasts or muscle stem cellsAm J Physiol Endocrinol Metab, 2014 (PMID 24253050)
- PubMed search: mechano growth factor IGF-1Ec musclePubMed / NCBI
- Expression and splicing of the insulin-like growth factor gene in rodent muscle is associated with muscle satellite (stem) cell activation following local tissue damageJ Physiol, 2003 (PMID 12692175)
- Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulationJ Physiol, 1999 (PMID 10087355)
- PubMed search: mecasermin recombinant IGF-1 clinical usePubMed / NCBI
Cite this page
PepCue. “MGF: the evidence.” PepCue, reviewed June 1, 2026. https://www.pepcue.app/p/mgf.
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