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MGF

The 24-amino-acid tail of an exercise-induced IGF-1 splice variant, injected locally on the theory that it wakes up satellite cells for repair and growth.

Also known as mechano growth factor, IGF-1Ec, IGF-1 splice variant, MGF E-domain peptide

Animal data only — Rodent or other animal studies. Dose translation to humans is genuinely uncertain.

The IGF-1Ec splice response to mechanical loading in muscle is real and well documented. Whether the synthetic 24-mer E peptide does anything useful when injected is not settled: some rodent cardiac and muscle work is positive, at least one careful myoblast study was flatly negative, and there are no human trials.

How it works

Mechanical loading and damage cause skeletal muscle to splice IGF-1 into the Ec isoform, whose distinctive C-terminal E domain is the 24-residue sequence sold as MGF. In rodent and cell work this peptide promotes myoblast proliferation while delaying differentiation, which is the signature of satellite cell mobilisation, and it has clear anti-apoptotic and cardioprotective effects after experimental myocardial infarction. Importantly, the E peptide appears to act independently of the IGF-1 receptor - the proposed receptor has never been definitively identified, which is a real gap. A 2014 study in myoblasts and primary muscle stem cells found no apparent effect of the synthetic peptide at all, so the mechanism is genuinely contested rather than merely under-studied.

Targets: Muscle satellite cells, Unidentified E-peptide receptor, ERK1/2 and FAK signalling (reported)

Dosing

ProtocolDoseFrequencyRoute
Post-workout local injectionImmediately post-workout, split across the trained muscle. Some protocols wait 30-60 minutes after a GHRP/GHRH dose.200 mcg – 400 mcgonce daily on training daysintramuscular
Injury-site protocolNear the injured site.200 mcg – 250 mcgonce dailysubcutaneous
  • · Entirely anecdotal. Given a serum half-life of minutes, anything other than local immediate-post-training injection has no coherent rationale.
  • · Extrapolated from rodent repair models; no human evidence.

Cycling

Common practice is 3-6 weeks alongside a training block. No evidence supports any particular duration.

Work out your exact syringe units →

Pharmacology

Half-life
Only a few minutes in serum - it is rapidly degraded, which is the whole reason PEG-MGF exists.
Onset
No reliable onset data exist. Anecdotal reports describe local fullness immediately and nothing objective thereafter.
Routes
intramuscular, subcutaneous
Molecule
Synthetic 24-amino-acid E-domain peptide of the IGF-1Ec splice variant
Sequence length
24 amino acids
Molecular weight
2867 Da

Handling

Diluent
Bacteriostatic water
Typical mix
1 or 2 mL
Vial sizes
2, 5 mg
Lyophilised
Fridge or freezer; room temperature is tolerated only briefly in transit.
Reconstituted
Refrigerated and used within about 2-3 weeks.
Light sensitive
Yes — keep it out of the light

Mixing

A 2 mg vial in 2 mL gives 1000 mcg/mL, so 200 mcg is 20 units on a U-100 syringe. Swirl gently.

Side effects

  • commonInjection-site pain and swelling— Local intramuscular injection into freshly trained muscle stings.
  • commonUnknown long-term risk— There is no human safety dataset of any kind. The honest answer is that nobody knows.
  • uncommonTransient flushing or headache— Reported anecdotally, mechanism unclear.

Do not use if

  • Active malignancy - proliferative signalling in an unproven peptide is a bad combination.
  • Pregnancy and breastfeeding.
  • Known hypersensitivity.

Combining it

  • redundantpeg-mgf — Same peptide, different pharmacokinetics. Running both is pointless.
  • synergyigf-1-des — A common post-workout local pairing; the synergy is theoretical only.

What to monitor

  • · No established bloodwork. Track the trained or injured tissue objectively - strength, range of motion, imaging if a real injury is involved.

Legal status

Not approved for human use. Sold as a research chemical and prohibited in sport by WADA as a growth factor.

References

  • Goldspink and colleagues, mechano growth factor and the IGF-1Ec splice response to mechanical loading (review) (review)
  • 2014 study in Am J Physiol reporting the MGF E peptide had no apparent effect on myoblasts or primary muscle stem cells (preclinical)
  • Rodent studies of MGF E-domain peptide delivery after experimental myocardial infarction (preclinical)

Mechanism in depth

The important and rarely stated fact about MGF is that it probably does not work through the IGF-1 receptor at all. Mills and colleagues, working with the synthetic MGF-Ct24E peptide on human myogenic precursor cells, presented evidence that the responses they saw proceed through a mechanism that does not involve IGF1R. What the peptide demonstrably does in cell culture is act as a motogen: it enhances expression of urokinase plasminogen activator, its receptor uPAR, and MMP-7 while reducing PAI-1 activity, without touching MMP-2 or MMP-9. That is a coherent pro-migratory programme - loosen the pericellular matrix so myogenic precursors can move - and it fits the biology that made the molecule interesting, which is that mechanical loading and damage induce the IGF-1Ec splice variant in muscle before the systemic IGF-1Ea response. Collins showed different regions of the MGF prohormone drive migration and proliferation of human mesenchymal stem cells, and Mavrommatis found the E-domain region inhibits apoptosis and preserves cardiac function after myocardial infarction in a rodent model. So the mechanistic story is real, but it is a story about cell migration, anti-apoptosis and precursor recruitment, not about protein synthesis. Nothing in it predicts hypertrophy in a trained adult, and the receptor mediating the effect has never been identified. Every dose, timing and site protocol in circulation was invented downstream of a mechanism nobody has closed.

What usually goes wrong

The dominant problem is that MGF is one of the most misrepresented products on the grey market. It is a short, highly basic, easily synthesised peptide, which makes it cheap to make badly - truncated sequences, high trifluoroacetate content and endotoxin contamination all show up as the same clinical picture, which is a hot, red, painful injection site and a flu-like few hours. People read that as 'the MGF is working'. It is not a documented pharmacological effect of the peptide. The second problem is the protocol folklore: post-workout timing within a specific number of minutes, site-specific injection into the trained muscle, and the claim that MGF must be run before PEG-MGF, all of which are inventions with no experimental basis. The third is the sunk-cost pattern of running MGF for months inside a stack and crediting it for results driven by the training, the food and the other compounds.

Bloodwork worth running

MarkerWhenWhy it matters
Serum IGF-1Baseline and at four weeks if stacked with anything that touches the GH axis.Not because MGF raises it - there is no evidence it does - but because people run MGF inside GH or IGF-1 stacks and then attribute whatever they see to the MGF. A baseline and on-cycle IGF-1 tells you which compound is actually doing anything.Act if: An IGF-1 above the age-adjusted reference range is about the stack, not the MGF, and the stack is what needs adjusting.
High-sensitivity CRPBaseline, then 24-48 hours after a dose during the first week.The most commonly reported subjective effect of MGF is a systemic inflammatory-feeling response - flushing, malaise, injection-site reaction. A CRP tells you whether that is real or expectation.Act if: A CRP that climbs above roughly 3 mg/L on-cycle in someone who was clear at baseline is a reason to stop and look at product quality.
Creatine kinaseBaseline and after two weeks of site injection.MGF is injected intramuscularly at volume into small muscles more often than almost any other compound in this class, and repeated local trauma shows up here. It also separates real muscle damage from ordinary training soreness.Act if: A CK several times the upper reference limit without a plausible training explanation means stop injecting into that site.

Pharmacokinetics

Metabolism
Presumed rapid peptidase degradation in plasma and tissue. The peptide is highly basic and contains multiple arginine and lysine residues, which are trypsin-like protease targets.
Elimination
Presumed renal filtration of fragments. Not measured.

Receptor targets

  • Unidentified MGF E-peptide receptor — Unknown. No receptor has been cloned or characterised, and no binding constant exists.

    Pro-migratory and anti-apoptotic signalling in myoblasts and mesenchymal stem cells, with upregulation of uPA, uPAR and MMP-7 and reduced PAI-1 activity.

  • IGF-1 receptor (IGF1R) — Not a ligand at meaningful affinity

    Mills reported the myogenic precursor cell response occurs through a mechanism that does not involve IGF1R. Vendors who market MGF as an IGF-1 receptor agonist are describing a molecule this is not.

What to expect, and when

Nothing systemic that is attributable to the peptide. Local injection-site reactions within minutes to hours, and those are as likely to reflect product quality as pharmacology. No timeline for any hypertrophic effect can be given, because no such effect has been demonstrated in a human.

Stacking and comparisons

MGF is almost never run alone, which is precisely why nobody can say what it does. The standard construction is MGF immediately post-workout on top of a GH or GH-secretagogue base, sometimes with IGF-1 LR3 on the same days. Mechanistically the pairing that makes the most sense on paper is MGF with something that actually drives protein synthesis, on the logic that MGF recruits and mobilises precursors while the IGF-1 analogue or GH does the anabolic work - but that division of labour has never been tested in a human. What you should not do is run MGF and PEG-MGF in the same week and then form a view about either. If you want to know whether MGF does anything for you, it has to be the only variable you changed, which almost nobody does.

Against PEG-MGF: the pegylated version was created to solve the assumed proteolysis problem, which trades the one mechanistic argument MGF has - a brief local pulse at the site of mechanical damage, mimicking the transient IGF-1Ec splice response - for a long systemic exposure that no longer resembles the biology it was modelled on. If you believe the MGF story at all, plain MGF is the version that fits it. Against IGF-1 DES, which occupies the same post-workout local-injection slot: DES has a defined receptor, decades of animal pharmacology and measured clearance data. MGF has three cell-culture papers and a rodent infarct study. Against BPC-157 or TB-500 as tissue-repair agents, MGF is in the same evidentiary tier - real preclinical signals, zero human data - but with the additional problem that the receptor is unidentified.

Rough cost

$40–$120/month. 2 mg vials commonly run 20-45 USD grey market, and typical anecdotal protocols consume roughly 2-4 mg a month. It is cheap, which is part of why it stays in circulation.

Genuinely uncertain

  • The receptor mediating MGF E-peptide activity has never been identified. Without it there is no affinity, no dose-response and no basis for any dosing protocol.
  • No pharmacokinetic data exist in any species for the synthetic MGF-Ct24E peptide. Half-life figures in circulation are guesses.
  • Whether the peptide survives subcutaneous or intramuscular administration long enough to reach any target is unknown. It is short, unprotected and rich in basic residues.
  • All the supporting biology is in vitro or in rodent injury models. There is no human study of MGF for any indication.
  • The C-terminal STFEEHK segment is reported consistently across the MGF literature as arising from the IGF-1Ec frameshift; the full-length human IGF-1Ec isoform sequence was not independently resolved from a database entry in this session, so the first 17 residues are confirmed against UniProt P05019 while the final seven rest on the published MGF-Ct24E literature.
  • Molecular weight is not given in the Core record and no authoritative value was resolved.

Papers