MGF splice variant expression after mechanical overload [1]
Well established in human and animal muscle — the IGF-1Ec isoform is upregulated following resistance exercise and damage.
PrecisePep/Peptide Library/PEG-MGF
Growth Hormone & Anabolic Support
PEG-MGF
pegylated mechano growth factor · IGF-1Ec · MGF · mechano growth factor
A splice variant of IGF-1 that muscle produces when mechanically damaged — pegylated to survive long enough to be injected, on the theory that supplying the signal beats earning it.
00 Overview
MGF is what muscle makes when you damage it. Mechanical overload triggers alternative splicing of the IGF-1 gene, producing IGF-1Ec — an isoform with a distinct C-terminal E-domain. That E-domain peptide appears to act independently of the IGF-1 receptor, activating satellite cells and driving them to proliferate before differentiating. It is one of the more elegant pieces of exercise biology.[1]
Native MGF has a half-life measured in minutes, because it is meant to act locally and briefly at the site of damage. Pegylation — attaching polyethylene glycol — extends that to days, which makes injection practical and simultaneously destroys the local, transient character that defines the endogenous signal.
The human evidence is essentially absent. There is real molecular biology here and real rodent work. There is no meaningful human interventional data for MGF or PEG-MGF, and the pegylated form is a research-chemical product rather than anything that has been through development.[2]
Pegylation changes what the molecule is for
MGF is a burst signal at a damage site. A pegylated version circulating for days is not that — it is a sustained systemic growth-factor signal wearing the name of a local one. Whether the biology survives that transformation has not been examined.
// Mechanism of action
Alternative splicing of IGF-1. Mechanical loading and damage shift IGF-1 gene splicing toward the Ec isoform in skeletal muscle. The resulting E-domain peptide is the active entity of interest.
Satellite cell activation. MGF is reported to activate quiescent satellite cells and drive proliferation, expanding the pool of myogenic precursors before they fuse into existing fibres — the proliferative phase that precedes differentiation.
Receptor-independent action. The E-domain appears to act through a mechanism distinct from the IGF-1 receptor, which is what makes MGF conceptually separate from IGF-1 rather than simply a variant of it. The receptor has not been identified.
Pegylation. PEG attachment reduces renal clearance and proteolysis, extending half-life from minutes to days. It also increases molecular size, which affects tissue distribution in ways nobody has characterised for this molecule.
01 Reported benefits
Effects that have been reported. A study-tier entry means a result was published — not that the effect is established, reproducible, or transferable from a rodent to a person.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
Satellite cell activation in models [1]
The E-domain peptide activates and expands satellite cell populations in cell culture and rodent work.
Muscle repair and regeneration in animal models [2]
Reported improvements in regeneration after injury, including in dystrophic and aged muscle models.
Cardiac regeneration signals in animal work [2]
MGF has been examined in cardiac repair models, with reported protective effects.
No human interventional data for MGF or PEG-MGF
No trial has administered either form to a human.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Enhanced muscle growth and repair in humans
The use case, extrapolated from satellite cell biology. Untested in humans in any form.
Localised effect from site injection
Widely believed and directly undercut by pegylation, which is designed to keep the molecule circulating systemically for days.
Post-workout timing to amplify the natural signal
The common rationale — dose when endogenous MGF would be rising. Coherent for the native peptide; less so for a version with a multi-day half-life.
Synergy with IGF-1
Proliferation then differentiation is a real sequence in myogenesis. Combining two growth factors also compounds the growth-factor exposure question.
Concern: sustained growth-factor signalling
The same proliferative and anti-apoptotic concern that attaches to IGF-1, applied to a molecule engineered for extended circulation.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Muscle fullness and pump
The characteristic report, and largely indistinguishable from fluid and glycogen effects.
Perceived faster recovery
Reported, uncontrolled and confounded by every other variable in a training programme.
Highly inconsistent effects
Reported variability is high, which is unsurprising given no established dose and no human pharmacokinetics.
Product identity concerns
Whether a vial contains pegylated MGF, unpegylated MGF, or an E-domain fragment is difficult to verify, and the pegylation is not visible in a standard purity assay.
Frequently reported as ineffective
Non-response is common, and for a compound with no human dosing data that is the expected outcome.
02 Adverse effects & risks
Adverse effects, contraindications and unknowns. The grey-market tier is where under-reporting is worst: uncontrolled use produces no systematic safety surveillance at all, so absence of a reported harm is not evidence of safety.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No human safety data
No toxicology, pharmacokinetics or adverse-event data in humans for either MGF or the pegylated form.
PEG accumulation is a recognised pharmaceutical concern [3]
Polyethylene glycol accumulation and anti-PEG antibody formation are documented considerations for pegylated therapeutics generally, and are assessed formally during drug development — which this has not undergone.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Sustained growth-factor exposure
Proliferative signalling circulating for days rather than acting locally for minutes.
Anti-PEG immunogenicity
Antibodies against the PEG moiety can accelerate clearance and, in some contexts, cause hypersensitivity. Uncharacterised here.
Additive with IGF-1 or GH secretagogues
Stacking growth-factor signalling from multiple directions compounds the same concern.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Injection-site reactions
Commonly reported.
Lethargy after dosing
Occasionally reported.
Few systemic complaints
Reflecting low usage and short exposures as much as anything else.
03 Dosing ranges
Figures below are documented, not recommended. Study ranges come from published protocols in the stated model; grey-market ranges are what the research community reports using and carry no safety validation of any kind.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No human dose exists [2]
Animal work uses weight-normalised local or systemic dosing of native MGF. Nothing converts to a human PEG-MGF schedule.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
The pegylated form does not need frequent dosing
A multi-day half-life is the whole point of pegylation. Daily dosing of a pegylated molecule accumulates.
Site injection is not doing what people think
Pegylation is designed to keep the molecule systemic. Injecting into a target muscle adds risk without a clear mechanistic gain.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
200–400 mcg, 2–3× weekly
The common community range, often post-training.
Site-specific intramuscular injection
Widely practised on the localisation belief.
4–6 week courses
Typical course length.
| Approach | Dose | Frequency | Route |
|---|---|---|---|
| Standard | 200 mcg | 2–3× weekly | Subcutaneous |
| Higher-end | 400 mcg | 2–3× weekly | Subcutaneous or IM |
04 Synergy & interactions
Combination effects. Almost no peptide combination has been studied as a combination in humans; stack logic is overwhelmingly mechanistic inference and community practice. Each linked compound has its own page.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No combination studies exist
None.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
With IGF-1 LR3
Proliferation then differentiation is a genuine myogenic sequence. It also stacks two growth-factor signals, which compounds the proliferative concern.
With GH secretagogues
Common in performance stacks. Same additive growth-factor logic.
With mechanical loading
The one accompaniment with real evidence — MGF expression is driven by loading, and satellite cell activation without a mechanical stimulus has nothing to organise around.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
Stacked with IGF-1 LR3 and GH secretagogues
The typical performance-stack context.
05 Protocols
Whole schedules — dosing, titration, cycle length, and off-time — as documented in trials, as proposed from mechanism, and as circulated in the research community. Reproduced for study and comparison only.
Highest confidenceReported in peer-reviewed literature, registered clinical trials, or regulatory filings. Note the model: much peptide literature is in vitro or rodent work, not human trial data.
No human protocol exists
No registered trial for MGF or PEG-MGF.
Unproven — inference onlyExtrapolated from a known mechanism, receptor profile, or adjacent compound class. Biologically plausible but not directly demonstrated for this compound in this context.
Progressive mechanical loading is the actual driver
MGF is downstream of loading. A protocol without a serious training stimulus is supplying a signal with nothing to act on.
Uncontrolled reportsAggregated from research-community logs, forums, vendor literature and self-reported experience. Uncontrolled, unverified, subject to placebo, polypharmacy and product-purity confounds. Lowest evidentiary weight.
4–6 weeks, 2–3× weekly post-training
The general community pattern.
Not part of either documented protocol
Neither documented protocol includes it.
05b Condition-specific interest
PEG-MGF has the thinnest evidence base of anything in the growth-hormone section and the most confident marketing. It is worth being precise about what is actually known, because almost nothing is.
No approval, no trial
No human trial of PEG-MGF exists for any indication. The underlying biology — mechano-growth factor as a splice variant of IGF-1 upregulated by mechanical loading — is real and interesting. Everything downstream of that, including whether a pegylated synthetic version reproduces any of it in a person, is unestablished.
Theorized — rodent, and the premise is genuine
Muscle repair and satellite cell activation
Pathophysiology
Mechanical loading damages muscle fibres, and repair depends on satellite cells activating, proliferating and fusing to the existing fibre. That is the step MGF is proposed to accelerate.
Mechanistic rationale
MGF is a genuine splice variant of the IGF-1 gene, produced locally in muscle in response to loading and damage. The biology is well described. What is not established is that injecting a pegylated synthetic peptide reproduces the effect of a locally produced, transiently expressed splice variant — the natural version acts locally and briefly, and pegylation is designed to do the opposite.
Community reports
Post-workout local injection is the usual pattern, on the reasoning that MGF acts locally. Site-specific fullness is commonly reported and is consistent with local irritation and fluid as readily as with hypertrophy.
Components carrying the argument: IGF-1Ec splice variant, pegylated
Theorized — and mass separates from function here too
Sarcopenia and muscle wasting
Pathophysiology
Age-related muscle loss involves reduced satellite cell number and responsiveness alongside anabolic resistance.
Mechanistic rationale
The rationale is coherent on paper and has no human evidence at all. The pattern across this entire axis — clearest in the ROMANA cachexia trials, where lean mass rose and handgrip strength did not — is that interventions on this pathway move mass more reliably than they move function.
Community reports
Almost entirely used by people already training hard, in whom loading is doing most of the work and attribution is impossible.
Components carrying the argument: Satellite cell activation
Theorized — and it is an IGF-1 analogue
The IGF-1 liabilities, inherited
Pathophysiology
IGF-1 receptor signalling drives proliferation and suppresses apoptosis, and cross-reacts with the insulin receptor at sufficient concentration.
Mechanistic rationale
PEG-MGF is a variant of IGF-1. The oncological caution that applies to IGF-1 LR3 applies here in principle, and pegylation extends exposure rather than limiting it. The hypoglycaemia risk is likely lower given the different receptor affinity profile, but "likely lower" is doing a great deal of work in a compound with no human pharmacokinetic data.
Community reports
Rarely raised. The absence of reported problems in a compound nobody has studied is not evidence of safety.
Components carrying the argument: IGF-1 family signalling
| Question | Position |
|---|---|
| Human trials? | None, for any indication |
| Is MGF real biology? | Yes — a genuine load-induced IGF-1 splice variant |
| Does injecting it reproduce that? | Unknown — the natural version is local and transient |
| What pegylation does | Extends exposure — the opposite of the natural pattern |
| Oncological caution | Applies — it is an IGF-1 variant |
| Best evidence for muscle | Resistance training, which produces MGF endogenously |
What actually has evidence for these conditions
Resistance training upregulates MGF endogenously. That is how the splice variant was discovered, and it remains the only intervention demonstrated to produce it in the right place, at the right time, in a person. Progressive overload with 1.2–1.6 g/kg/day of protein has the evidence for both mass and function, and it is the comparator this compound has never been tested against.
06 Handling, reconstitution & storage
Physical-chemistry reference for laboratory handling of the lyophilised material. Reproduced so that stability and concentration mathematics can be studied — see the calculator for the arithmetic and the reconstitution guide for sterile technique.
Reconstitution
Supplied lyophilised, commonly 2 mg per vial. Reconstituted with bacteriostatic water.
Storage
Lyophilised: −20 °C. Reconstituted: 2–8 °C.
Common vial sizes
Commonly 2 mg lyophilised vials.
Stability notes
Whether a vial actually contains pegylated material is not verifiable by a standard purity assay, and pegylation is what the product name is selling.
07 Legal & regulatory status
Regulatory status changes and differs by country. This is a summary for orientation, not legal advice — check your own jurisdiction.
Not approved anywhere. Neither MGF nor PEG-MGF has been through clinical development. Supplied as a research chemical.
Regulatory update — current as at August 2026
PEG-MGF is scheduled for review by the FDA's Pharmacy Compounding Advisory Committee before the end of February 2027, alongside Melanotan II, LL-37 (cathelicidin), Dihexa acetate and PEG-MGF — whichever of those is not this compound.
This follows the FDA's April 2026 restructuring of the Section 503A categories and the July 2026 meeting at which six peptides (BPC-157, KPV, TB-500, MOTS-c, Semax and Epitalon) were recommended for the Bulks List and one (emideltide/DSIP) was not. Nothing has been decided for PEG-MGF.
A PCAC recommendation is not an approval, and the 503A Bulks List is not a drug approval either. It is also worth knowing that July 2026 was the second round: across two sittings in October and December 2024 the same committee reviewed seven substances — among them ipamorelin, kisspeptin-10, AOD-9604, CJC-1295 and thymosin alpha-1 — and rejected all seven. Two separate things are being conflated in almost every write-up of the 2026 decision:
- The vote is advisory. PCAC recommendations are non-binding. The pathway from here runs: removal from Category 2 (done, April 2026) → PCAC recommendation (done, July 2026) → placement in Category 1 through notice-and-comment rulemaking, which commonly takes eight to twelve months → and the HHS Secretary must sign off on any addition to the list. Nothing is lawfully compoundable on the strength of the vote alone.
- Even a successful listing would not make these approved drugs. Inclusion on the 503A Bulks List permits a licensed compounding pharmacy to use the substance in a compounded preparation for an individual patient with a prescription. It says nothing about the compound being demonstrated safe and effective — no efficacy trial is required, and none of these has one.
- It would not legitimise research-chemical supply. A compounding pathway runs through a licensed pharmacy and a prescriber. Grey-market vials labelled "research use only" are not that, and nothing in this decision changes their status.
Regulatory and trial claims re-checked against primary sources on 16 August 2026. Checked: pending PCAC review, expected before end of February 2027. Approvals, trial readouts and compounding decisions move faster than anything else on this page — a date here means someone looked, not that nothing has changed since.
Anti-doping
Growth factors including IGF-1 variants and mechano growth factor are explicitly named on the WADA Prohibited List under S2. Prohibited at all times.
§ Sources & further reading
Links resolve to PubMed records, trial registries, publisher pages or primary documents. Where a body of work rather than a single paper is cited, the link opens a PubMed query so the full result set — including newer papers than this page — can be reviewed. Verify every claim against the primary source before relying on it.
- PubMed: mechano growth factor / IGF-1Ec — splice variant expression and satellite cell activation (live query)Database or literature search
- PubMed: MGF in muscle regeneration and cardiac repair models (live query)Database or literature search
- PubMed: anti-PEG antibodies and pegylated therapeutic immunogenicity (live query)Database or literature search
- WADA Prohibited List (current edition) — S2 growth factorsRegulatory / official document
Reminder
For educational and research reference only. Nothing on this site is medical advice, a recommendation, or an instruction to administer any substance to a human being. Every figure on this page is a record of what has been reported, not a recommendation. Full disclaimer.