FDA looked for human exposure data on PEG-MGF by any route of administration and found none. PEG-MGF also has no defined molecular weight, because PEG is a polymer with a chain-length distribution rather than a single molecule.
Those two problems compound each other. A compound with no clinical record can still be characterised; a compound that cannot be characterised cannot even be tested properly. PEG-MGF sits in the growth hormone peptides category, its PEG-MGF compound page carries 27 independent lab tests, and the underlying biology — a muscle-specific IGF-1 splice variant — is entirely real.
Has PEG-MGF been tested in humans?
No. FDA's published evaluation states the agency "has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration," and that it "lacks important information regarding any safety issues raised by PEG-MGF." ClinicalTrials.gov returns one study when PEG-MGF is searched as an intervention, NCT02375620, and that trial is of pegylated somatropin — an entirely different product. A search on "mechano" as an intervention returns 14 studies, none of them MGF.
The regulator's sentence is worth reading twice, in full:
"FDA has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration. FDA lacks important information regarding any safety issues raised by PEG-MGF, including whether it would cause harm if administered to humans."
That is a formal review reaching a null result, not an absence of interest. No registered human trial of MGF or PEG-MGF exists, and FDA arrived at the same conclusion independently through its own literature review.
The practical consequence is underestimated. Every dose, every injection interval and every "post-workout timing" protocol circulating for PEG-MGF was invented. There is no human pharmacokinetic study to base an interval on, no dose-ranging study to base a quantity on, and no safety study at all. The PEGylation is specifically intended to extend half-life — and nobody has measured what that half-life is in a person.
Why does PEG-MGF have no molecular weight?
Because PEGylated products do not have one. PEG is a polymer built from repeating ethylene oxide units of 44 daltons each, and a manufacturing batch contains chains of varying length distributed around a mean, so a PEGylated peptide is a family of species separated by 44 Da steps rather than a single molecule. We searched for a defined specification — pharmacopoeial monograph, regulatory specification, chemical registry entry — and found none. Any certificate quoting one number is quoting something that does not exist as a specification.
PEGylation itself is legitimate and widely used: several approved biologics are PEGylated, and attaching polyethylene glycol to slow clearance is standard pharmaceutical practice. Polydispersity is not a defect in the technique. It is a property of polymers, and approved PEGylated products handle it by specifying the distribution rather than a single mass.
Nothing in this market specifies a distribution. A vendor quoting "PEG-MGF MW = X" is quoting either a nominal average that carries no verification power, or a number they invented, and there is no way for a buyer to tell which.
FDA's own language points at the same gap. The agency notes that PEG-MGF "may have complexities with regard to peptide-related impurities and API characterization" — API characterisation being the regulatory term for knowing what your active ingredient is.
What is mechano growth factor?
Mechano growth factor is IGF-1Ec, a real alternative splice product of the IGF-1 gene expressed in muscle after mechanical loading and damage. From UniProt P05019, isoform 4 replaces precursor positions 152–195 with the seven residues STFEERK, giving a 158-residue isoform. The MGF peptide sold in this market is the C-terminal 24 residues of that E-domain, roughly 2,850 daltons. The splice variant is verifiable; everything PEGylated downstream of it is not.
From the verified UniProt data, that 24-residue peptide is:
YQPPSTNKNTKSQRRKGSTFEERK
The biology behind it is not in dispute. An alternative splice of the IGF-1 gene, induced in skeletal muscle by mechanical loading and damage, is a well-described phenomenon, and it is the reason this compound has a plausible-sounding story attached to it. The distance between that story and the material in a vial is the subject of the rest of this article.
Which MGF sequence is in the vial — …STFEERK or …STFEEHK?
We could not determine that, and nobody in this market appears to have noticed the question. UniProt's human IGF-1 isoform 4 gives the E-domain ending …STFEERK with arginine; the sequence quoted almost universally on vendor pages and in forums ends …STFEEHK with histidine. That is a difference of 19 daltons on a molecule of roughly 2,850 — trivially detectable by mass spectrometry. Two different sequences circulate under the same name, and nobody appears to be checking which is in the vial.
Attribute | Reference MGF (UniProt isoform 4) | Marketed MGF | PEG-MGF |
|---|---|---|---|
E-domain terminus |
|
| Whichever peptide was PEGylated |
Peptide length | 24 residues (C-terminal E-domain) | 24 residues | 24 residues plus polymer |
Mass | ~2,850 Da | 19 Da different | No single mass — polydisperse |
PEGylation | None | None | Present, degree unverifiable |
On FDA's tables | Neither table | Neither table | "Nominated but withdrawn" |
We are not asserting that the market sequence is wrong. Arg-to-His differences can reflect species variants, isoform annotation history, or a propagated transcription error. What we can say is that the reference sequence and the marketed sequence disagree by one residue and 19 daltons, and that a bare "MGF" specification is therefore ambiguous. See mass spectrometry for peptides for what that test would settle if anyone ran it against a stated target.
What can a certificate of analysis establish for a PEGylated peptide?
Less than for any other compound on this platform. Mass spectrometry on a PEGylated product returns an envelope rather than a peak, with no single expected mass to match. HPLC is similarly compromised, because different PEG chain lengths have different retention behaviour, so genuine PEGylated material does not give one clean peak. And the degree of PEGylation — whether the product is PEGylated once, multiple times, at the intended site, or not at all — cannot be verified by anything offered in this market.
That last point deserves emphasis, because it is the one buyers never see addressed. Establishing whether, where and how often PEG is attached requires specialised analytical methods, and we have not seen those methods offered by any vendor or third-party laboratory serving this market. The attribute that defines the product is the attribute nobody measures.
For the underlying methods and how to read what a laboratory actually reports, see what HPLC testing can and cannot tell you and red flags in peptide certificates of analysis.
Which PEG-MGF claims survive the evidence?
Three of ten. MGF is a genuine IGF-1 splice variant, it is genuinely expressed after mechanical loading, and PEG-MGF is genuinely prohibited under WADA S2.3 — those hold. The rest fail: the …STFEEHK sequence is disputed by 19 daltons, a single molecular weight is not a real specification for a polydisperse product, human testing has never happened by FDA's own finding, every circulating dose was invented, and a clean purity result is a warning rather than a confirmation.
Claim | Evidence | Verdict |
|---|---|---|
MGF is a real IGF-1 splice variant | UniProt P05019 isoform 4 (IGF-1Ec) | True |
MGF is expressed after mechanical loading | Established biology | True |
Sequence ends …STFEEHK | UniProt human isoform 4 gives …STFEERK | Disputed — 19 Da apart |
PEG-MGF has molecular weight X | PEG is polydisperse; no defined MW exists | Not a real specification |
Tested in humans | FDA: "not identified any human exposure data... via any route" | Never |
Has an evidence-based dose | No human PK or dose-ranging study exists | Invented |
PEGylation extends half-life in humans | Never measured in a person | Unverified |
Purity testing confirms it | PEGylated products do not give one clean peak | False |
On FDA's Category 2 list | In the "nominated but withdrawn" table | Outdated |
Banned in sport | WADA S2.3 — "Mechano growth factors (MGFs)" | True |
Two of the three surviving claims are about the endogenous splice variant, not about the product. The third is a prohibition.
Where does PEG-MGF stand with FDA and WADA?
PEG-MGF is not on FDA's active Category 2 list. On the page current 22 April 2026, "Mechano growth factor pegylated (PEG-MGF)" appears in the second table, "Bulk drug substances nominated but withdrawn" — a withdrawal by the nominator, which is a procedural event rather than a safety clearance. Non-PEGylated MGF appears on neither table. PEG-MGF has no USP monograph and is not a component of any approved drug, and WADA section S2.3 prohibits mechano growth factors at all times.
FDA's retained language on the page current 22 April 2026, in full:
"Compounded drugs containing Mechano Growth Factor Pegylated (PEG-MGF) may pose significant risk for immunogenicity for certain routes of administration and may have complexities with regard to peptide-related impurities and API characterization. FDA has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration. FDA lacks important information regarding any safety issues raised by PEG-MGF, including whether it would cause harm if administered to humans."
Only the PEGylated form was ever nominated, which is why plain MGF is absent from both tables rather than cleared by either. PEG-MGF satisfies none of the three statutory routes for 503A compounding. For how nominations, withdrawals and category assignments have moved, see our FDA peptide regulation timeline.
WADA names this class explicitly. Section S2.3, "Growth factors and growth factor modulators," prohibits "Mechano growth factors (MGFs)" alongside "insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues," FGFs, HGF, PDGF, thymosin-β4 and VEGF. Prohibited at all times. That is a named category, not an S0 inference, and published doping-control methods for peptidic drugs in blood samples explicitly cover mechano growth factors. See do peptides show up on drug tests.
What do 27 lab tests show, and why is a 100.00% purity result a warning?
The Purity Index records PEG-MGF at 99.38% average across 27 tests (verified August 2026), from Chromate, ILS, MZ Biolabs, Ethos Analytics and Vanguard, across 219 verified shops, with individual results running from 98.35% to 100.00%. That top figure deserves scrutiny rather than confidence: a genuinely PEGylated peptide carries a polymer chain-length distribution and should not resolve as a single perfect peak. One vendor's March 2026 sample was labelled 5 mg and tested at 6.35 mg.
A 100.00% HPLC result is more consistent with a non-PEGylated peptide, or with an assay not designed for this material, than with a well-made PEGylated product. We are not accusing any vendor of anything. We are pointing out that on this specific compound, the usual reassuring signal reads differently, and that a buyer treating it as reassurance is drawing the wrong inference.
The 6.35 mg result against a 5 mg label is a 27% overage, which on a compound with no established dose is a dosing error nobody can size.
PEG-MGF price data shows 13 shops in stock, median $18.99/mg, lowest $12.50/mg on a 2 mg vial (verified August 2026), with vial prices from $25.00 to $94.97. Those figures exclude shipping, taxes and customs, coupon codes, bulk tiers, multi-vial kits and account-gated pricing. Those figures sit inside a platform tracking 530 shops and 11,852 independent lab tests across 118 peptides, with 1,283 community reviews (verified August 2026).
Check | What it can establish | Reality for PEG-MGF |
|---|---|---|
Mass spectrometry | Mass against a reference | No defined reference mass exists — PEG is polydisperse |
Degree of PEGylation | Whether, where and how often PEG is attached | Not offered by anyone in this market |
Sequence | …STFEERK or …STFEEHK | The two differ by 19 Da; nobody is checking |
HPLC purity | Homogeneity | A perfect peak is a warning, not a reassurance, here |
Fill accuracy | Vial matches label | A 27% overage is on record |
Endotoxin (LAL) | No pyrogens — FDA's stated immunogenicity concern | Rarely reported |
Compare vendors on the PEG-MGF compound page, and read the wider body of independent lab tests for how coverage on this compound compares.
How does PEG-MGF compare with the other growth-factor compounds?
PEG-MGF is the hardest of four related compounds to verify. It sits alongside IGF-1 LR3, IGF-1 DES and follistatin, all four explicitly named in WADA's prohibited list, and none of them has a verifiable mass in this market: PEG-MGF because PEG is polydisperse, LR3 because no reference mass could be verified, DES because no authoritative mass was located, and follistatin because of species and glycoform ambiguity. That combination is close to the worst configuration a buyer could face.
Compound | Human data | Verifiable mass | WADA |
|---|---|---|---|
PEG-MGF | FDA: none identified, any route | No — polydisperse | S2.3, "MGFs" |
Zero registered trials | No reference mass we could verify | S2.3, "its analogues" | |
Zero registered trials | No authoritative mass located | S2.3, "its analogues" | |
Gene therapy only, no results posted | Which species? Glycoforms | S4.3, named |
Hard to authenticate and easy to detect in a doping test is an unusual pairing, and it is the defining commercial fact about this group. PEG-MGF is the extreme case, because its unverifiability is a property of the chemistry rather than a gap in the record.
The trial that would settle this
The trial that would settle PEG-MGF cannot begin without a product specification, because there is currently nothing to test against: the PEG species distribution and attachment site would have to be defined first. Resolving whether commercial MGF is …STFEERK or …STFEEHK comes next, then a Phase 1 measuring human pharmacokinetics and the half-life PEGylation is supposed to deliver, anti-drug antibody testing for FDA's stated immunogenicity concern, and muscle function as the primary endpoint.
Element | Requirement | Why |
|---|---|---|
Product specification | Define the PEG species distribution and attachment site | There is currently no specification to test against |
Sequence resolution | Establish whether commercial MGF is …STFEERK or …STFEEHK | A 19 Da ambiguity in the marketed product |
Phase 1 | Human pharmacokinetics | FDA found no human exposure data of any kind |
Half-life | Measure what PEGylation actually achieves | It is the entire rationale, never measured in humans |
Immunogenicity | Anti-drug antibody testing | FDA's stated concern for this specific substance |
Primary endpoint | Muscle function, not satellite cell markers | The mechanism is not the outcome |
The first row is not a formality. A PEGylated biologic entering trials requires a characterised product — defined PEG size, defined attachment chemistry, defined species distribution. None of that exists for the material sold here.
Frequently Asked Questions
Has PEG-MGF been tested in humans?
No. FDA's published evaluation states the agency "has not identified any human exposure data on drug products containing PEG-MGF administered via any route of administration." ClinicalTrials.gov returns no genuine PEG-MGF study.
Why can't you give a molecular weight?
Because PEGylated products do not have one. PEG is a polymer with a chain-length distribution, so the product is a family of species separated by 44-dalton ethylene oxide units rather than a single molecule. We searched for a defined specification — pharmacopoeial, regulatory, or registry — and found none.
What does a high purity result mean on PEG-MGF?
Less than usual, and possibly the opposite of what it appears to mean. A genuinely PEGylated peptide carries a polymer distribution and should not resolve as one perfect peak. A 100.00% HPLC result is more consistent with a non-PEGylated peptide or an unsuitable assay than with well-made PEGylated material.
Is the MGF sequence I see online correct?
We could not determine that. The sequence quoted almost everywhere ends …STFEEHK with histidine; UniProt's human IGF-1 isoform 4 gives …STFEERK with arginine. The difference is 19 daltons — easily detected by mass spectrometry, and apparently not being checked by anyone.
What dose should I use?
There is no evidence-based answer. No human pharmacokinetic study, no dose-ranging study and no safety study exists. Every protocol in circulation was invented, including the timing conventions.
Is PEG-MGF banned in sport?
Yes, explicitly. WADA section S2.3 prohibits "mechano growth factors (MGFs)" at all times, and published doping-control methods for peptidic drugs in blood cover them.
Where PEG-MGF sits
PEG-MGF combines two problems that rarely appear together: no human data at all, by FDA's own finding across any route of administration, and a compound that cannot be verified even in principle by the tools available. PEGylation makes the molecular weight a distribution rather than a number, a clean HPLC peak may indicate the PEG is not there, and the underlying peptide sequence is itself disputed by 19 daltons. The biology is real; nothing downstream of it is.
Either problem alone would make this a hard compound to justify. FDA did not write that it had concerns about PEG-MGF; it wrote that it "lacks important information regarding any safety issues raised by PEG-MGF, including whether it would cause harm if administered to humans." That is the language of a regulator with no information at all, which is a different position from a regulator with a mild concern.
A muscle-specific IGF-1 splice variant induced by mechanical loading is genuine and interesting biology. Everything downstream of it, in this market, is unverifiable and untested.
Browse the growth hormone peptides category, or our complete peptide guide with 118 compounds (verified August 2026). Compare shops through independent lab tests and community-verified shop reviews.
This article is for educational and informational purposes only and does not constitute medical advice. Peptides discussed may be investigational compounds not approved by the FDA (or equivalent regulators in your jurisdiction) for human use. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.
