MGF / PEG-MGF

Mechano growth factor, IGF-1Ec (human) / IGF-1Eb (rodent), MGF E-peptide, PEG-MGF (pegylated MGF)

Growth hormone axis

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Summary

Class: MGF is a naturally occurring splice variant of the IGF-1 gene made by muscle after loading. "MGF" as sold is a synthetic 24-amino-acid peptide corresponding to the variant's unique C-terminal E-domain; PEG-MGF is the same peptide with a polyethylene-glycol chain attached to slow clearance
Mechanism: Proposed to activate muscle satellite (stem) cells and delay their differentiation, expanding the pool available for repair — through a receptor that has never been identified
Routes studied: Gene transfer and intramuscular injection in rodents; cell culture; subcutaneous and intramuscular (community)
Dose range reported: Rodent: single intramuscular injections of ~10–100 µg or plasmid gene delivery. Community: 200–400 µg PEG-MGF subcutaneous or intramuscular 2–3 times weekly, or 100–200 µg unpegylated MGF after training. No human dose exists
Half-life: Unpegylated E-peptide: minutes in plasma (community cites 5–7 minutes). PEG-MGF: community cites 48–72 hours; neither figure has been established in humans †
Storage: Lyophilised: refrigerate, protect from light. Reconstituted: refrigerate, use within ~4 weeks (community practice)
Regulatory status: Not approved for human use anywhere

Doses are as reported in studies or by the community — never recommendations.

1What it is

When a muscle is stretched or damaged, it briefly switches the way it processes the IGF-1 gene and produces a variant called IGF-1Ec, which Geoffrey Goldspink's group at University College London named "mechano growth factor" in the late 1990s. The variant has the normal mature IGF-1 core plus a different tail (the E-domain) because of a frame shift in the final exon. Goldspink proposed that this tail is itself a signalling peptide, acting separately from IGF-1 to activate satellite cells before the classic IGF-1 pathway takes over to build protein.

The product sold as "MGF" is a synthetic copy of just that 24-amino-acid tail, not the whole growth factor. PEG-MGF adds a polyethylene-glycol chain so the fragment survives in the blood for longer. Both are synthetic research compounds; the natural MGF is a full-length protein made inside muscle cells and is not injected anywhere in nature.

Whether the isolated E-peptide does anything on its own is genuinely contested. Most positive data come from one group using gene delivery of the full variant or from cell-culture work, and independent attempts to show a stand-alone effect of the E-peptide have had mixed results.

2How it's thought to work

Satellite-cell activation. in culture, the E-peptide increased proliferation of C2C12 myoblasts and delayed their fusion into fibres, in theory expanding the stem-cell pool for later growth (Yang & Goldspink 2002).

Independent of the IGF-1 receptor. effects in culture persisted with IGF-1 receptor blockade, implying another, unknown receptor. None has been identified more than 20 years on.

Two-phase model. MGF rises within hours of loading and falls within a day or two; systemic IGF-1Ea rises later. The community rationale for "MGF after training, PEG-MGF between sessions" is built on this model.

Possible non-muscle roles. neuroprotection and cardiac protection in rodents; the full variant is also expressed in bone, tendon and brain.

A splice variant of IGF-1 produced by muscle after damage, thought to act on satellite cells so they divide and repair the fibre. PEGylation is an attempt to make its minutes-long life usable.Schematic — not to scale

3What the research shows

Muscle hypertrophy by gene transfer

injection of a plasmid encoding MGF produced a ~25% increase in muscle fibre cross-sectional area within three weeks in mice, faster than the same vector encoding IGF-1Ea (Goldspink 2001; Barton 2002). This is gene delivery of the whole variant, not injection of a peptide. [2]

Synthetic E-peptide in cell culture

The isolated E-domain peptide increased myoblast proliferation and inhibited differentiation in C2C12 cells (Yang & Goldspink 2002, FEBS Lett). Human muscle cells from older donors showed a reduced response (Hameed 2003). Other groups have reported that effects attributed to the E-peptide are weak or absent, and that MGF's actions may be carried mostly by its mature IGF-1 core (Fornaro 2014, Am J Physiol Endocrinol Metab; Matheny 2010, Endocrinology review). [3][4][7][8]

Graded B (physiology, not treatment)

Expression in human muscle

Human biopsy studies show MGF mRNA rises after resistance exercise and that this response is blunted in older adults, while GH administration increased it (Hameed 2003, J Physiol; Hameed 2004, J Physiol). These establish that MGF is part of human muscle adaptation, not that injecting the peptide does anything. [4][5]

Neuroprotection and cardiac repair

Rodent models of motor neuron injury, ischaemic stroke and myocardial infarction report protection with MGF or its E-peptide (Dluzniewska 2005, FASEB J; Carpenter 2008, Heart Lung Circ). [6]

Injected MGF or PEG-MGF in humans

No published human study. Community use for muscle growth and recovery rests on mechanism, animal gene-transfer data and anecdote.

4Reported side effects and interactions

Literature-reported

No human safety data. Animal gene-transfer studies did not focus on adverse effects.

Community-reported

injection-site soreness and swelling, mild hypoglycaemia-like symptoms (likely a cross-over from stacked IGF-1 LR3 rather than MGF), headache, water retention; many report no noticeable effect.

Theoretical. any agent that stimulates satellite-cell proliferation carries a theoretical tumour-growth concern; the unidentified receptor means off-target effects cannot be predicted; PEG chains occasionally cause anti-PEG antibody reactions.

Interactions. none established. Frequently stacked with IGF-1 LR3, GH and anabolic steroids in community protocols — none studied together.

Markers researchers commonly monitor

No compound-specific marker exists; there is no validated assay for injected E-peptide and no human pharmacology to interpret one. Markers that follow from the physiology:

Marker	Why it's watched
IGF-1	to detect whether a stacked compound, not MGF, is driving systemic effects.
Fasting glucose	relevant mostly because of common co-use with IGF-1 LR3.
Creatine kinase (CK)	a marker of muscle damage/turnover if tracking recovery.
Baseline CBC and CMP	general, with the note that nothing compound-specific is established.

Free for everyone. Safety information is never behind a paywall.

5Reconstitution and handling

Usually supplied in 2 mg (MGF) or 2–5 mg (PEG-MGF) vials. with , swirl gently. Community protocols for unpegylated MGF dose immediately post-training because of its very short plasma life.

Open in calculator, pre-loaded →

6Commonly studied alongside

IGF-1 LR3 (community pairing based on the two-phase model), GH secretagogues. In research, compared against IGF-1Ea gene transfer.

Informational cross-links. Not stack recommendations.

7Regulatory status by region

Region	Status (checked —)
United States	Not FDA-approved; not eligible for compounding
European Union	Not authorised
United Kingdom	Not licensed
Australia	Not approved; growth factors are prescription-only (Schedule 4) †
South Africa	Not registered
Sport (WADA)	Prohibited (S2 — MGF is explicitly named among growth factors)

8Open questions

Does the isolated E-peptide have a biological effect at all, or does MGF act through its IGF-1 core?
What receptor, if any, binds the E-peptide?
Pharmacokinetics of PEG-MGF in humans — unknown.

9References

1Goldspink G (1999). Changes in muscle mass and phenotype and the expression of autocrine and systemic growth factors by muscle in response to stretch and overload. J Anat. PubMed · DOI
2Barton ER, Morris L, Musaro A, Rosenthal N, Sweeney HL (2002). Muscle-specific expression of insulin-like growth factor I counters muscle decline in mdx mice. J Cell Biol. PubMed · DOI
3Yang SY, Goldspink G (2002). Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Lett. PubMed · DOI
4Hameed M et al. (2003). Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. J Physiol. PubMed · DOI
5Hameed M et al. (2004). The effect of recombinant human growth hormone and resistance training on IGF-I mRNA expression in the muscles of elderly men. J Physiol. PubMed · DOI
6Dluzniewska J et al. (2005). A strong neuroprotective effect of the autonomous C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia. FASEB J. PubMed · DOI
7Matheny RW, Nindl BC, Adamo ML (2010). Minireview: Mechano-growth factor: a putative product of IGF-I gene expression involved in tissue repair and regeneration. Endocrinology. PubMed · DOI
8Fornaro M et al. (2014). 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. PubMed · DOI

† Being confirmed by our reviewers against current sources.

10Community

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Self-reported side effects Phase 2

Not enough data yet. 0 of the 50 members needed have logged this compound for 4+ weeks. We don't show anything below 50, so no one can be identified.

11Page history

25 Oct 2026Profile published — awaiting medical review

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