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PEG-MGF

Also known as pegylated mechano growth factor, PEGylated IGF-1Ec E-peptide, long-acting MGF

MGF with a polyethylene glycol chain attached; the long half-life it is sold on has never been measured.

preclinical Recovery & tissue research chemical

At a glance

Category
Recovery & tissue
Status
research chemical
Route
subcutaneous
Half-life
Unknown. No pharmacokinetic study of PEG-MGF has been published in any species. Figures of 48-72 hours, or of several days, appear on vendor pages and clinic material and trace to no primary source.
Onset
unknown
Molecular weight
Not determinable. The peptide contributes approximately 2849 g/mol; total mass depends entirely on the undisclosed PEG chain.
Sequence
YQPPSTNKNTKSQRRKGSTFEEHK, covalently modified with a polyethylene glycol chain. Neither the PEG molecular weight nor the attachment site is disclosed by suppliers, and there is no reason to assume different products are the same molecule.

Not approved for human use anywhere. The FDA lists "Mechano growth factor pegylated (PEG-MGF)" by name among bulk drug substances that may present significant safety risks, stating it "may pose significant risk for immunogenicity for certain routes of administration" and that the agency "has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration". As of the agency's April 2026 update it sits in the "nominated but withdrawn" table, having previously been in category 2 of the interim 503A/503B policies 3.

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 peptide component is the MGF E-domain, and its proposed mechanism is discussed in the MGF entry: satellite cell activation independent of the IGF-1 receptor, with no identified receptor of its own and a documented failure to replicate the core cell-culture findings. Pegylation does not change that mechanism; it is a formulation strategy, not a pharmacological one.

Pegylation - attaching a polyethylene glycol polymer - is a well-established technique in protein therapeutics. It increases hydrodynamic radius, which slows renal filtration, and it shields the backbone from proteases. Approved pegylated products such as pegfilgrastim and peginterferon demonstrate that the principle works. The extension achieved, however, depends critically on PEG size, whether the chain is linear or branched, and where on the molecule it is attached. It is not a fixed multiplier that can be assumed.

It is also not free. Pegylation frequently reduces receptor binding and intrinsic potency, and can impede cell entry. For a small, highly cationic peptide whose putative activity may depend on entering cells, attaching a large inert polymer is as likely to interfere as to help. Whether PEG-MGF retains any of the activity attributed to MGF has not been tested and published.

What the research shows

There is no published research on PEG-MGF. A PubMed search returns no study of this compound - the handful of results for the term concern unrelated pegylated IGF-1 constructs. The entire commercial case for it rests on a pharmacokinetic claim that nobody has measured, applied to a peptide whose activity has itself failed replication.

Research in humans

No published human study of PEG-MGF exists, of any design, for any indication. There is likewise no human study of unmodified MGF.

Animal and lab research

No published animal study of PEG-MGF. The rodent work cited in its marketing was performed with unmodified MGF E-domain peptide, frequently by local or sustained delivery rather than systemic injection.

Caveats. Two compounding problems. First, the underlying peptide's foundational claim was directly contradicted by Fornaro and colleagues in 2014, who found no effect of MGF on myoblast proliferation or differentiation at concentrations up to 500 ng/ml 1. Second, the specific selling point of the pegylated version - a half-life measured in days rather than minutes - has no published basis whatsoever, in humans or animals. Pegylation of an inactive peptide produces a long-lasting inactive peptide. There is additionally no product characterisation: with the PEG size and conjugation site undisclosed, purchasers cannot know what they have, and vials from different suppliers are not necessarily comparable.

What it is used for

  • Sold as a longer-acting alternative to MGF, injected less frequently for the same claimed satellite cell effects
  • Used in bodybuilding protocols alongside growth hormone secretagogues or IGF-1 analogues, with no data on any combination
  • No research or clinical use

Dosing

Dose
user protocols quote 200-400 mcg per administration
Frequency
typically two to three times per week, sometimes once weekly
Route
subcutaneous
Duration
cycles of 4-6 weeks in circulated protocols
  • These figures come exclusively from bodybuilding protocols and vendor pages. No dose-finding study exists, and the FDA states it has identified no human exposure data for PEG-MGF by any route 3.
  • The reduced injection frequency compared with MGF rests entirely on the unpublished half-life claim. If that claim is wrong, the schedule is wrong, and there is no published measurement either way.
  • Because the PEG chain is an undisclosed fraction of the total mass, a stated dose in micrograms does not tell you how much peptide is delivered. Two products both labelled 400 mcg may differ substantially in peptide content.

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

Protocols

Twice-weekly cycle

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.

Weeks 1-4 to 6200-400 mcg per administration, two to three times per week subcutaneously; some protocols use a single weekly injection
After the cyclea break of comparable length before repeating

The lower frequency compared with unmodified MGF rests entirely on an unpublished half-life claim for the pegylated form; nothing has been measured either way. The microgram figure is also not comparable between products, because the PEG chain makes up an undisclosed share of the stated mass.

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. No stability data have been published for this conjugate; customary shelf-life periods are convention. Lyophilised powder frozen, protected from light.

Worked example

2 mg vial + 2 ml bacteriostatic water = 1 mg/ml. 400 mcg = 0.4 ml, i.e. 40 units on a U100 insulin syringe. Note that the labelled mass may refer to the conjugate, not the peptide.

Do not shake. Pegylated peptides in solution can foam readily; let the diluent run down the vial wall and swirl gently.

Work it out for PEG-MGF

Safety

Side effects

  • Injection site reactions, reported anecdotally as more pronounced and longer-lasting than with unmodified MGF
  • Anti-PEG antibodies are a documented phenomenon with pegylated therapeutics and can cause accelerated clearance or hypersensitivity reactions; this has never been assessed for PEG-MGF. The FDA separately flags immunogenicity risk for this substance, along with peptide-related impurities and difficulty characterising the active ingredient 3
  • No controlled human safety data exist. The FDA states it "has not identified any human exposure data" for PEG-MGF by any route and "lacks important information regarding any safety issues raised by PEG-MGF, including whether it would cause harm if administered to humans" 3

Do not use if

  • Active or previous malignancy - the IGF-1 pathway origin of the peptide makes this a poor choice, and the concern is unquantified
  • Pregnancy and breastfeeding: no data
  • Children and adolescents: no data
  • Known hypersensitivity to polyethylene glycol
  • 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 4

Interactions

Not systematically studied. No interaction data exist. The theoretical interaction most worth naming is with other pegylated products, since anti-PEG immunity raised against one can in principle affect the clearance of another.

Sources