MGF (Mechano Growth Factor)

How does MGF work?

MGF is the E-domain peptide of the IGF-1Ec splice variant. When muscle is mechanically loaded or damaged, the IGF-1 gene is spliced differently to produce this variant. The PROPOSED action — distinct from mature IGF-1 — is to activate satellite/muscle stem cells and promote myoblast proliferation while delaying terminal differentiation, expanding the myonuclear pool available for repair, with mature IGF-1Ea acting later to drive differentiation and fusion. This mechanism is contested: the core positive findings come largely from one research group and were NOT reproduced by an independent lab (Fornaro 2014 [5]), which found no effect of synthetic MGF E-peptide.

1. Mechanosensitive splicing [1][2]. In mechanically stretched or loaded muscle, the IGF-1 gene is alternatively spliced to produce the IGF-1Ec variant (MGF), which is essentially absent at rest. Stretch combined with electrical stimulation is the strongest stimulus for this splice variant, and MGF appears to be regulated differently from the systemic IGF-1Ea isoform.
2. Proposed E-peptide action [3]. The distinct MGF E-domain peptide has been reported to increase myoblast proliferation while delaying terminal differentiation — the opposite of what mature IGF-1 does. The proposed physiological role is to expand the pool of activated satellite/muscle stem cells before mature IGF-1Ea drives their differentiation and fusion into existing fibers.
3. A separate receptor is proposed [3]. In the original cell work, blocking the classical IGF-1 receptor (IGF-1R) did not abolish the E-peptide effect, which led the authors to suggest MGF may act through a receptor OTHER than IGF-1R. The identity of any such receptor remains unresolved.
4. CONTESTED — failed independent replication [5]. This mechanism rests largely on cell-culture and rodent work from a single primary group (Goldspink and colleagues). When an independent industry laboratory (Fornaro 2014, Novartis) tested synthetic MGF E-peptide, it found NO effect on myoblasts or primary muscle stem cells — directly contradicting the proliferation/anti-differentiation claims. The mechanism should therefore be treated as proposed and unresolved, not established.
5. MGF vs PEG-MGF. Native MGF E-peptide has a very short half-life (minutes), which limits systemic action. PEG-MGF is a synthetic research peptide with PEG attached to extend half-life so it circulates longer. The rationale for PEG-MGF is entirely pharmacokinetic and theoretical — there is no controlled human trial of administered PEG-MGF, and no controlled human data on injected native MGF. Extended exposure does not establish a benefit.

What is MGF used for?

MGF has no approved use. Its evidence base is overwhelmingly preclinical and concerns endogenous biology rather than an administered drug: discovery of the mechanosensitive splice variant, a single group's claim that the E-peptide drives proliferation and delays differentiation, and — importantly — an independent null result that failed to reproduce that claim. The only human data measure the body's own MGF gene expression after exercise, not injected peptide. There is no controlled human efficacy trial of MGF or PEG-MGF.

1. Discovery of the splice variant [1]. The founding observation was that an alternatively spliced IGF-1 mRNA (later called MGF/IGF-1Ec) appears in mechanically stretched muscle but is essentially absent at rest — establishing that IGF-1 splicing is mechanosensitive.
2. Differential regulation by load [2]. In rabbit muscle, stretch plus electrical stimulation was the strongest stimulus for the MGF variant, and MGF was regulated differently from systemic IGF-1Ea — reinforcing the idea of a load-responsive local isoform.
3. Proposed pro-proliferation effect [3]. In C2C12 muscle cells, the MGF E-peptide reportedly increased myoblast proliferation while delaying differentiation, with an effect that persisted despite IGF-1R blockade. This is the central positive claim for MGF's supposed muscle-repair role.
4. Contradicting null result [5]. A well-powered independent laboratory found synthetic MGF E-peptide had no apparent effect on myoblasts or primary muscle stem cells, directly contradicting the proliferation claim and showing the finding is not robustly replicated across labs.
5. Human data are about endogenous expression only [4]. The few human datasets measure the body's own MGF mRNA after heavy resistance exercise — which rose in young but not elderly men. This describes an endogenous adaptive response to exercise, NOT the effect of an administered MGF or PEG-MGF peptide. No controlled human trial of injected MGF/PEG-MGF exists.

How long does MGF take to work?

There is no evidence-based answer. No controlled human trial has measured a time course for administered MGF or PEG-MGF, so any timeline claim would be extrapolation from cell and rodent studies (some of which failed to replicate) or from anecdote. Native MGF's half-life is only minutes; PEG-MGF is designed to circulate longer, but its human pharmacokinetics have not been verified in peer-reviewed work.

There is no established, evidence-based time course for MGF or PEG-MGF in humans. No controlled human trial has characterized onset, duration, or magnitude of any effect from an administered MGF/PEG-MGF peptide. Native MGF is cleared within minutes, which is the rationale offered for pegylation, but PEG-MGF's human pharmacokinetics have not been verified in peer-reviewed studies. Community timelines exist but are anecdotal and are not supported by controlled data. Treat any specific “weeks to results” claim as unverified.

How is MGF dosed?

There is NO established, evidence-based dose for MGF or PEG-MGF. No controlled human pharmacology exists to define a dose, route, or frequency. Any specific figures below are drawn ENTIRELY from bodybuilding/anecdotal community sources — not from peer-reviewed research — and are presented only to describe what the community reports. They are not a recommendation and are not evidence.

How is MGF administered?

There is no evidence-based administration protocol for MGF or PEG-MGF. In community use it is handled like other research peptides — reconstituted with bacteriostatic water and injected subcutaneously or intramuscularly with a small insulin syringe — but no route, timing, or dose has been validated in humans. For the general mechanics of insulin syringes, units vs mcg, and subcutaneous technique, see the syringes and injection technique guide. The reconstitution table below is illustrative arithmetic only — it is NOT a recommended dose.

What does MGF stack well with?

There is no controlled human data on any MGF or PEG-MGF stack. In community contexts MGF is discussed alongside other IGF-1 variants and GH secretagogues on the theory that it acts locally on satellite cells while those compounds raise systemic IGF-1/GH — but this rationale is theoretical and, given the failed replication of MGF's core mechanism, may rest on an effect that does not occur. Treat all stacking claims as speculative.

1. IGF-1 variants (theoretical). IGF-1 DES and IGF-1 LR3 are discussed alongside MGF in community contexts on the idea that MGF acts locally while these raise IGF-1 signaling more broadly. No controlled human stack data exists.
2. GH secretagogues (theoretical). Ipamorelin and MK-677 raise endogenous GH and, downstream, IGF-1. They are sometimes discussed with MGF on the theory of pairing systemic GH/IGF-1 with a proposed local repair signal — again, without controlled data.
3. Follistatin (theoretical). Follistatin is discussed in the same muscle-hypertrophy community conversations, on a myostatin-inhibition rationale distinct from MGF's. There is no human evidence for combining the two.
4. Important caveat. Because MGF's core pro-proliferation mechanism failed independent replication (Fornaro 2014), any stack built around that mechanism may be predicated on an effect that does not occur in practice.

What are the side effects of MGF?

Human safety for MGF and PEG-MGF is essentially uncharacterized — there are no controlled human safety studies of the injected peptide. The risks below are therefore a mix of general injection risks and theoretical growth-factor concerns rather than a documented adverse-event profile. Most 'reported effects' circulating in communities are anecdotal.

Does MGF interact with other drugs?

There is no human interaction data for MGF or PEG-MGF. No drug-drug interaction studies have been conducted. The only interactions that can be discussed are theoretical, based on shared biology with the IGF-1 axis and insulin signaling.

1. No human interaction studies exist. There is no controlled data on how MGF or PEG-MGF interacts with any other drug or peptide.
2. Theoretical IGF-axis overlap. Because MGF derives from an IGF-1 splice variant, it is theoretically part of the IGF-1 signaling landscape; combining it with other IGF-1 variants or with GH secretagogues that raise IGF-1 could, in principle, compound growth-factor signaling. This is speculative, not documented.
3. Theoretical insulin overlap. IGF-1 and insulin signaling pathways overlap; any theoretical metabolic effect of an IGF-derived peptide would warrant caution alongside insulin or other glucose-lowering agents. No human data confirm a real interaction.

How should MGF be stored?

1. Lyophilized (powder) form: Store at -20°C for long-term storage; refrigerate at 2–8°C for short-term.
2. Reconstituted solution: Store at 2–8°C; use within 28–30 days.
3. Reconstitute with bacteriostatic water for injection (BAC water). Swirl gently — do not shake.
4. Never freeze reconstituted solution.
5. Protect from light. Store in original carton.
6. Discard if cloudy, discolored, or contains particles.

What are the limitations of MGF research?

This is the most important section on the page. The MGF evidence base is weak and internally contradicted: the core positive findings trace to a single research group and failed independent replication, all human data concern endogenous gene expression rather than injected peptide, and PEG-MGF's case is purely pharmacokinetic. There is no human safety data, research-grade purity is unverified, and MGF is WADA-prohibited.

Where to source MGF

MGF and PEG-MGF are not FDA-approved and are sold only as research-grade peptides. In PP's vetted directory, they are currently listed by the vendor highlighted below, which publishes batch documentation and carries both the native and pegylated forms.

MGF FAQ

References

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. https://pubmed.ncbi.nlm.nih.gov/8884603/
2. McKoy G, Ashley W, Mander J, Yang SY, Williams N, Russell B, Goldspink G. Expression of insulin growth factor-1 splice variants and structural genes in rabbit skeletal muscle induced by stretch and stimulation. J Physiol. 1999;516(Pt 2):583-592. https://pubmed.ncbi.nlm.nih.gov/10087355/
3. 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. https://pubmed.ncbi.nlm.nih.gov/12095637/
4. Hameed M, Orrell RW, Cobbold M, Goldspink G, Harridge SDR. 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. https://pubmed.ncbi.nlm.nih.gov/12562960/
5. 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. https://pubmed.ncbi.nlm.nih.gov/24253050/

Published Studies