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MGF

Also known as mechano growth factor, IGF-1Ec, IGF-1 Ec E-domain peptide, MGF-24aa

The 24-amino-acid E-domain of a mechanically induced IGF-1 splice variant; its muscle effects failed replication.

preclinical Recovery & tissue research chemical

At a glance

Category
Recovery & tissue
Status
research chemical
Route
subcutaneous or intramuscular, in practice near the trained muscle
Half-life
No published human pharmacokinetics. An unmodified, highly basic 24-residue peptide is expected to be cleared within minutes; the figure of 'a few minutes' quoted widely is a plausible inference rather than a measurement in humans.
Onset
unknown
Molecular weight
approximately 2849 g/mol, calculated from the 24-residue free-acid sequence; suppliers quote a range of values and rarely state the salt form
Sequence
YQPPSTNKNTKSQRRKGSTFEEHK (human MGF E-domain, 24 amino acids)

Not approved for human use anywhere. Sold as a research chemical. The pegylated version, "Mechano growth factor pegylated (PEG-MGF)", is named by the FDA among bulk drug substances that may present significant safety risks - previously category 2 under the interim 503A/503B policies, and in the "nominated but withdrawn" table as of the agency's April 2026 update - with the agency noting it has identified no human exposure data for it by any route 5. The unmodified peptide is not on any FDA bulks list either, so it is likewise not a compoundable substance.

Doping status: Prohibited (WADA S2.3, growth factors - "Mechano growth factors (MGFs)")

Checked against the WADA 2026 Prohibited List. For a specific product and country, Global DRO is the lookup athletes are expected to use — the List names substances, not brand names.

Mechanism of action

The IGF-1 gene is alternatively spliced. The dominant circulating product is IGF-1Ea; mechanical loading and muscle damage transiently induce a different splice variant, IGF-1Ec in humans (IGF-1Eb in rodents), which the Goldspink group named mechano growth factor. A 49-base-pair insert causes a reading frame shift, producing a distinct C-terminal extension peptide of 24 residues in humans - the E-domain. On post-translational processing this E-domain is separated from the mature IGF-1 portion.

The hypothesis that made MGF commercially interesting is that the isolated E-domain peptide has biological activity of its own, independent of IGF-1 and independent of the IGF-1 receptor: specifically, that it activates quiescent satellite cells, drives their proliferation and delays their terminal differentiation, thereby expanding the pool of myonuclei available for repair and hypertrophy. This is a satellite-cell recruitment story, not a direct anabolic-signalling story.

No receptor for the E-domain peptide has ever been identified. That is the central mechanistic weakness. Proposed intracellular interactions have been reported - including binding to 14-3-3 proteins in cardiomyocytes - but there is no accepted account of how an extracellularly injected peptide reaches such targets, and no defined signalling cascade.

The E-domain sequence also carries a nuclear localisation signal and is highly cationic, which means it can enter cells non-specifically. Effects observed in culture at high concentrations may reflect that property rather than a receptor-mediated action.

What the research shows

MGF is a real biological phenomenon: the splice variant exists, is mechanically induced, and is well documented in muscle, bone and heart. The claim that the isolated 24-residue E-peptide is an anabolic agent is a different matter, and it has been directly contradicted. A well-powered 2014 study from an industrial laboratory failed to reproduce the foundational satellite-cell findings and concluded that the physiological role of MGF as a distinct factor is in question 1. There are no human trials of the peptide.

Research in humans

There are no published human clinical trials of MGF, for any indication. The human-derived work is ex vivo: primary muscle progenitor cells from healthy, dystrophic and ALS donors have been exposed to synthetic MGF-24aa in culture, with reports of increased proliferation and fusion potential. Human expression studies show IGF-1Ec upregulation after resistance exercise and in conditions such as fibrostenotic Crohn's disease, but expression of a transcript is not evidence that injecting its E-peptide does anything.

Animal and lab research

Rodent work reports satellite cell activation, muscle hypertrophy after local delivery, and cardioprotection: E-domain peptide administration after myocardial infarction has been reported to reduce apoptosis, preserve contractility and delay decompensation, including via polymer microstructure delivery systems. Most of these studies use local or sustained delivery rather than systemic bolus injection, which is what users do.

Caveats. The replication failure is the dominant caveat and is usually omitted from vendor material. Fornaro and colleagues (2014, Am J Physiol Endocrinol Metab) tested MGF peptide at concentrations up to 500 ng/ml on myoblasts and primary muscle stem cells and saw no effect on proliferation and no inhibition of differentiation, explicitly calling into question whether MGF has a physiological role as a separate factor 1. Beyond that: no identified receptor, no human pharmacokinetics, no toxicology, and a large gap between sustained local delivery in animal models and weekly subcutaneous injection in practice.

What it is used for

  • Injected locally after resistance training in the belief that it recruits satellite cells to the trained muscle
  • Used alongside IGF-1 LR3 or growth hormone secretagogues in bodybuilding protocols, with no data on any such combination
  • Investigated preclinically for cardiac repair after infarction, where E-domain peptide administration delayed decompensation 3 and reduced apoptosis while preserving cardiac function 4 in rodent models, and for muscle regeneration in dystrophies

Dosing

Dose
user protocols quote 100-200 mcg per injection site
Frequency
typically immediately after training, on training days only, on the reasoning that the natural splice variant is transiently expressed after loading
Route
subcutaneous or intramuscular, near the trained muscle
Duration
cycles of 4-6 weeks in circulated protocols
  • These figures come entirely from bodybuilding protocols. No dose-finding study has been conducted in humans or, for systemic injection, in animals.
  • The post-workout timing rationale is an argument from the physiology of the endogenous splice variant, not a result from any study of injected peptide. It also assumes an effect that a 2014 replication attempt did not find: MGF peptide at up to 500 ng/ml had no apparent effect on myoblasts or primary muscle stem cells 1.
  • The local-injection practice assumes the peptide acts where it is placed. There is no distribution study in humans supporting or refuting that.

These figures describe what the literature and published protocols report. They are not advice and not a dosing instruction.

Protocols

Post-training injections

user protocol — not validated

Source: Bodybuilding protocols and vendor pages

This is not a validated schedule. It is a pattern that circulates among users and sellers, reproduced because it is what people actually follow — not because it has been tested. No trial established these doses, this interval or this duration, and nobody is checking what is in the vial. Treat every number below as an assertion, not a finding.

Training days, weeks 1-4 to 6100-200 mcg per injection site, immediately after the session, into or near the trained muscle
Rest daysno injection

The timing is reasoned from when the endogenous splice variant is expressed after mechanical loading, not from any measurement of the injected peptide. That reasoning has a prior problem: a 2014 replication attempt found no apparent effect of the peptide on myoblasts or primary muscle stem cells at all.

Schedules are reproduced as their source states them. Units, IU and milligrams explains why the figures are not interchangeable between products.

Reconstitution

Vial sizes
2 mg, 5 mg
Solvent
bacteriostatic water (0.9% benzyl alcohol)
Storage
Reconstituted at 2-8 °C. The customary few-week window is convention, not a published stability figure for this peptide. Lyophilised powder frozen, protected from light.

Worked example

2 mg vial + 2 ml bacteriostatic water = 1 mg/ml. 200 mcg = 0.2 ml, i.e. 20 units on a U100 insulin syringe.

Do not shake; let the diluent run down the vial wall. The peptide is strongly cationic and can adsorb to surfaces, so avoid unnecessary transfers.

Work it out for MGF

Safety

Side effects

  • Injection site pain, redness and swelling - commonly reported, plausibly related to the peptide's high positive charge
  • Transient local heat or itching
  • Immunogenicity has not been assessed for this peptide. The FDA flags immunogenicity risk, peptide-related impurities and characterisation difficulty for the pegylated form 5
  • No controlled human safety data exist. For the pegylated form the FDA states it has identified no human exposure data by any route and lacks the information to say whether it would cause harm in humans 5; nothing better exists for the unmodified peptide

Do not use if

  • Active or previous malignancy - IGF-1 pathway involvement makes any IGF-1-derived product a poor choice here, and IGF-1Ec overexpression has been described in several tumour types
  • Pregnancy and breastfeeding: no data
  • Children and adolescents: no data
  • Competitive athletes under the WADA code: prohibited at all times under S2.3, growth factors and growth factor modulators, which names "Mechano growth factors (MGFs)" as a non-Specified substance class 6

Interactions

Not systematically studied. No formal interaction studies exist. Combination with growth hormone, IGF-1 analogues or insulin is common in practice and entirely uncharacterised.

Sources