PEG-MGF

A longer-lasting copy of the repair signal your muscle makes after hard training.

Evidence: ELab & animal what's this?
Grade E for the injected compound. Human data only show that muscle makes natural MGF after exercise.
Also known as: PEGylated Mechano Growth Factor · IGF-1Ec · MGF E-domain peptide
Class: Synthetic PEGylated peptide based on a local IGF-1 splice variant

The 30-second version

WhatMGF, a local splice variant of IGF-1, with a PEG chain that stretches its life from minutes to days.

Why people use itPost-training repair and hypertrophy, often in sequence before IGF-1 LR3.

The honest catchNo human trial of injected MGF or PEG-MGF exists.

What it is

When training causes micro-damage, the muscle reads the IGF-1 gene differently and makes its own local repair molecule, mechano growth factor (IGF-1Ec in humans), which has a distinctive E-domain tail. Unlike liver IGF-1, MGF is made and used on the spot. Native MGF lasts only 5–7 minutes. Attaching polyethylene glycol (PEGylation) keeps it active for hours to days, which makes it practical to inject.

How it works

Damage. Hard training switches on MGF within the first couple of hours.

Peak at 2–6 h. MGF wakes satellite cells, the dormant muscle stem cells beside each fibre.

Proliferation. Through the E-domain and MAPK–ERK signalling, satellite cells multiply.

Hand-off. MGF fades and IGF-1Ea takes over the later protein-building phase.

Fusion. Satellite cells donate nuclei to fibres, so the muscle repairs and grows.

Unlike IGF-1 LR3, MGF acts locally on satellite cells and doesn’t have IGF-1’s whole-body insulin-like effects, so it carries little hypoglycaemia risk. That’s why the community runs it first (activate), then IGF-1 (build), copying the body’s own order.

What the research shows

In people: human muscle makes MGF after heavy resistance exercise, and the response is blunted in older muscle¹. That confirms its role, but it doesn’t test injection. In animals and cells: mostly from the Goldspink lab that discovered it. MGF activates and multiplies satellite cells and supports repair and hypertrophy, separately from mature IGF-1^2,3. Animal work also hints at benefits for tendon, heart and nerve tissue.

Real biology, well understood. The injected benefit is inferred, not demonstrated.

Evidence at a glance

Use	Grade	Best evidence	Main gap	Read
Natural MGF in muscle	BHuman trials	Made after resistance training¹	Own MGF, not injected	Real biology
Satellite-cell activation	ELab & animal	Activates and multiplies them^2,3	Preclinical	Well mapped
Injected muscle growth	DCommunity use	Community reports	No human trial	Unproven

Dosing: what has been reported

Not a recommendation. These figures describe what was studied or what circulates in practice, kept separate so you can see how solid each one is. Speak with a qualified clinician before acting on any of it.

Setting	Figure	Route	Grade
Published human	None	—	—
Community, PEG-MGF	200–500 mcg once or twice weekly, after training	SC or IM	D
Community, native MGF	~200 mcg immediately after training (minutes-long half-life)	SC or IM, local	D

Post-workout timing lines up with the natural window when muscle activates satellite cells. Without the training stimulus there’s little for it to act on.

Preparing & storing

Reconstitute with bacteriostatic water, refrigerate and don’t shake. PEGylation makes it much more stable than native MGF.

Reported side effects

Injection-site soreness, redness or a lump
Occasional mild fatigue or headache
Anti-PEG antibodies with repeated dosing, which can clear it faster and weaken the effect
No meaningful drop in blood sugar (unlike IGF-1 LR3)

Who should avoid it

Active or past cancer (IGF-1 receptor pathway)
Known PEG allergy
Pregnancy and breastfeeding
Tested athletes: WADA prohibited growth factor

Regulatory status checked Oct 2026

Body	Status	Detail
FDA (US)	Not approved	Research compound.
EMA (EU)	Not approved	No marketing authorisation.
CDSCO (India)	Not approved	No approval identified.
WADA	Prohibited	IGF-1-related growth factor; banned at all times.

The NexGen read

The body’s first repair signal, extended

PEG-MGF copies the opening step of muscle repair, and the biology is real. Whether injecting it adds anything beyond what hard training already triggers hasn’t been tested in people.

References

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(1):247–254.
Goldspink G. Mechanical signals, IGF-I gene splicing, and muscle adaptation. Physiology. 2005;20:232–238.
Chargé SBP, Rudnicki MA. Cellular and molecular regulation of muscle regeneration. Physiol Rev. 2004;84(1):209–238.