Summary
PEG-MGF is a synthetic copy of the E domain (end section) of mechano growth factor, an alternate form of the growth factor IGF-1 that human muscle makes briefly after resistance exercise or injury, with PEG attached (pegylated) so it lasts longer in the body. In cell studies the E domain peptide increases myoblast (muscle precursor cell) proliferation and delays their maturation, and in mice it preserved heart function after infarction (a heart attack), but no human trial of the synthetic peptide exists, so its evidence grade is animal-only. It has never been approved by FDA, its 503A nomination was withdrawn so it is off Category 2 (FDA's list of compounding ingredients with significant safety risks) but not on the bulks list of ingredients pharmacies may use, it cannot lawfully be compounded, and mechano growth factors are named on the WADA Prohibited List under section S2.
What is PEG-MGF?
PEG-MGF is a pegylated synthetic 24 amino acid peptide copying the E domain of mechano growth factor, a splice variant of IGF-1 (IGF-1Ec in humans) expressed in muscle after mechanical loading or damage. It is also known as Pegylated mechano growth factor, MGF, Mechano growth factor, IGF-1Ec E-domain peptide, IGF-1Eb (rodent MGF), MGF E-peptide.
How does it work?
Mechanical loading or damage of muscle shifts IGF-1 gene splicing toward the MGF isoform for roughly a day, after which splicing returns to the systemic IGF-1Ea form. The MGF E domain is thought to activate muscle satellite (stem) cells and increase myoblast proliferation while inhibiting terminal differentiation, acting through a receptor other than the IGF-1 receptor (blocking the IGF-1 receptor with an antibody did not remove the effect). Pegylation extends the half life of the otherwise rapidly cleared peptide. Whether an injected synthetic E domain peptide reproduces the effects of locally spliced MGF in humans has never been tested.
| Cluster | Tissue repair and healing |
|---|---|
| Routes | Subcutaneous or intramuscular injection (as sold); Intraperitoneal or intravenous (mouse study) |
| Conditions studied | Muscle recovery and injury; Muscle wasting and sarcopenia |
| Record | v2, draft, verified Sep 22, 2026 |
What does the evidence say about PEG-MGF?
Evidence is limited to in vitro myoblast studies, rodent muscle expression studies, one mouse myocardial infarction study of a synthetic E domain peptide, and human biopsy studies showing that MGF mRNA rises after resistance exercise in young but not elderly subjects. No human study has given PEG-MGF or any synthetic MGF peptide to people, and the pegylated product sold online has no published pharmacology at all. The human biopsy studies measured endogenous MGF expression and did not administer the peptide; they are listed but do not raise the grade.
| Evidence type | Indexed studies | Participants (human) |
|---|---|---|
| Human randomized trials | 0 | n/a |
| Human observational studies | 1 | 15 |
| Animal studies | 3 | n/a |
| All indexed studies | 4 | 15 |
Human evidence
No indexed human trial of PEG-MGF or any synthetic MGF peptide identified. The only human data are on the natural gene product: in 15 subjects (8 young, 7 elderly), MGF mRNA in quadriceps biopsies rose significantly 2.5 hours after high resistance exercise in the young group but not in the elderly, and resting MGF levels were about 100 fold lower than the IGF-1Ea isoform.
Animal evidence
In cultured myoblasts the MGF E domain increased proliferation and inhibited terminal differentiation, unlike mature IGF-1, and the effect persisted when the IGF-1 receptor was blocked. In mice, a synthetic MGF E domain peptide given at the time of myocardial infarction inhibited apoptosis, prevented pathologic hypertrophy, and preserved systolic and diastolic function at 2 weeks. Reviews describe MGF as a local muscle growth and repair factor whose expression falls with age and in dystrophic muscle.
Key studies
| Study | Design and population | Outcome | Grade |
|---|---|---|---|
| Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation2002 PMID 12095637 | In vitro myoblast cultureCultured muscle cells | The MGF E domain increased myoblast proliferation and inhibited terminal differentiation, unlike mature IGF-1, through a receptor other than the IGF-1 receptor | Evidence: Animal-only evidence |
| Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise2003 PMID 12562960 | Human muscle biopsy study before and after a single bout of resistance exercisen = 15 8 young (25 to 36 years) and 7 elderly (70 to 82 years) subjects | MGF mRNA rose significantly 2.5 hours after exercise in young but not elderly subjects; resting MGF was about 100 fold lower than IGF-1Ea | Evidence: Human observational evidence |
| The E-domain region of mechano-growth factor inhibits cellular apoptosis and preserves cardiac function during myocardial infarction2013 PMID 23712705 | Cell stress assays plus mouse myocardial infarction modelH9c2 cardiac cells and mice after coronary ligation | Synthetic E domain peptide inhibited apoptosis in vitro and, given at infarction, preserved systolic and diastolic function and reduced apoptotic nuclei at 2 weeks | Evidence: Animal-only evidence |
| Mechanical signals, IGF-I gene splicing, and muscle adaptation2005 PMID 16024511 | Narrative reviewAnimal and human studies of IGF-1 splicing in muscle | Describes MGF as a local growth and repair factor that kick starts hypertrophy after resistance exercise and whose expression is impaired in old age and disease | Evidence: Animal-only evidence |
Conditions studied
| Condition | Grade | Note |
|---|---|---|
| Muscle recovery and injury | Evidence: Animal-only evidence | Mechano growth factor splice variant; rodent and cell data only; WADA prohibited. |
| Muscle wasting and sarcopenia | Evidence: Animal-only evidence | Muscle cell and rodent data only; WADA prohibited. |
Is PEG-MGF legal in the United States?
FDA and compounding status
Never reviewed or approved by FDA for any use. PEG-MGF (mechano growth factor, pegylated) was nominated for the 503A bulks list and placed in 503A Category 2; the FDA Category 2 page current as of April 22, 2026 now lists it under bulk drug substances nominated but withdrawn, so it is no longer in Category 2 but is not on the bulks list and has no active nomination. It is not a component of an approved drug and has no USP monograph, so a 503A pharmacy has no lawful basis to compound it, and it is not eligible for 503B outsourcing. It is available only as a research chemical, which is not lawful for human use.
WADA status
WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.
Regulatory timeline
- WADA
WADA publishes the 2027 Prohibited List
WADA published the 2027 Prohibited List on September 21, 2026, and it takes effect January 1, 2027. The S2 peptide hormone and growth factor classes are unchanged. BPC-157 is still named under S0, and MOTS-c is still named under S4.4 as an activator of AMP-activated protein kinase. WADA added a note that many peptides without approval for human use fall under S0 or another section, and that a peptide not named on the list may still be prohibited. GLP-1 receptor agonists such as semaglutide and tirzepatide are still not on the list.
- FDA
FDA lists BPC-157 and 16 other peptides as withdrawn from 503A Category 2
FDA's Category 2 page, revised in April 2026 and current as of April 22, 2026, moved BPC-157, AOD-9604, CJC-1295, dihexa, DSIP, epitalon, injectable GHK-Cu, ipamorelin, KPV, LL-37, melanotan II, MOTS-c, PEG-MGF, selank, semax, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) to a list of bulk drug substances nominated but withdrawn by their nominators. A withdrawn substance is no longer in 503A Category 2, but withdrawal is not an approval and does not place a substance on the 503A bulks list; a 503A pharmacy still needs a listing before it may compound it. Ipamorelin acetate remains in 503B Category 2. Seven of the withdrawn peptides (BPC-157, KPV, TB-500, MOTS-c, semax, epitalon, and DSIP) were taken to the Pharmacy Compounding Advisory Committee in July 2026.
- WADA
WADA 2026 Prohibited List takes effect
The 2026 WADA Prohibited List took effect on January 1, 2026 and continues to prohibit the S2 peptide hormone and growth factor classes (GHRH analogs, growth hormone secretagogues, GH fragments, IGF-1 and analogs, MGF, thymosin beta-4 and derivatives, hCG and GnRH-class releasing factors in males), myostatin inhibitors, insulin and the AMPK activator MOTS-c under S4, desmopressin under S5, and BPC-157 under S0. GLP-1 receptor agonists such as semaglutide and tirzepatide are not on the list.
- WADA
WADA 2025 Prohibited List keeps peptide hormones and growth factors banned at all times
The 2025 WADA Prohibited List took effect on January 1, 2025. Section S2 (peptide hormones, growth factors, related substances and mimetics) covers GHRH analogs such as CJC-1295, sermorelin, and tesamorelin, growth hormone secretagogues such as ipamorelin, GHRP-2, GHRP-6, hexarelin, and ibutamoren (MK-677), growth hormone fragments such as AOD-9604, growth factors including IGF-1 and its analogs, MGF, and thymosin beta-4 (TB-500), and chorionic gonadotropin and releasing factors such as gonadorelin and kisspeptin (prohibited in males). Myostatin inhibitors such as ACE-031 fall under S4, insulin under S4 metabolic modulators, desmopressin under S5, and BPC-157 remains an S0 non-approved substance.
What published studies of PEG-MGF used
Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.
Not established in human literature. No human study has administered PEG-MGF or any synthetic MGF peptide. The mouse cardiac study used a synthetic E domain peptide at doses reported per animal that do not translate to humans.
Routes reported
| # | Route |
|---|---|
| 1 | Subcutaneous or intramuscular injection (as sold) |
| 2 | Intraperitoneal or intravenous (mouse study) |
What are the side effects and interactions of PEG-MGF?
Side effects
| # | Reported side effect |
|---|---|
| 1 | No human safety data of any kind |
| 2 | Injection site pain and swelling reported anecdotally |
| 3 | Theoretical concern about promoting growth of existing tumors, shared with IGF-1 family peptides (not studied) |
| 4 | Hypoglycemia is a class concern for IGF-1 related peptides, though the E domain acts through a different receptor and this has not been assessed |
Interactions
| # | Interaction |
|---|---|
| 1 | No formal human interaction studies exist |
| 2 | Often stacked with IGF-1 LR3 or growth hormone secretagogues in gray market use; no combination has been studied |
Contraindications
| # | Contraindication |
|---|---|
| 1 | Active cancer or history of cancer (theoretical growth factor concern) |
| 2 | Pregnancy and breastfeeding (no data) |
| 3 | Competitive athletes subject to WADA testing (prohibited at all times under S2) |
How do people access PEG-MGF legally?
Typical cost: Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity.
Verified access options
Step 1
No lawful United States access path identified on the last verified date; the 503A nomination was withdrawn and it is not on the bulks list.
Step 2
Not available as an FDA approved product and not eligible for 503B outsourcing.
Step 3
Products labeled research use only are not lawful for human use and are not verified for identity or purity.
Access paths are verified against public regulatory records and prescriber licensing. We never list unlicensed vendors.
Compare PEG-MGF
What's actually offered, and what that means for you
Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make PEG-MGF lawful. PEG-MGF is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [5] [7]
Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [7] [8] [9] [10] [11]
What changes for you
- No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [11]
- Identity, purity, sterility, and dose accuracy can vary from batch to batch. [7]
- Insurance rarely covers it, so you usually pay cash.
- For tested athletes, PEG-MGF is prohibited at all times on the WADA list, whatever the source. [6]
What to check
These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:
- A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [11]
- A real evaluation by a licensed prescriber, not just an online form.
- A certificate of analysis for the specific batch.
Frequently asked questions
Is PEG-MGF legal?
It is not an FDA approved drug. It was nominated for the 503A bulks list (ingredients pharmacies may use to compound drugs for individual patients) and placed in Category 2 (ingredients flagged for significant safety risks), and FDA now lists it as a withdrawn nomination; it cannot be compounded because it is not a component of an approved drug and is not on the 503A bulks list. The only products on the market are research chemicals, which are not lawful for human use. Possession is not a crime, but no licensed channel can lawfully supply it for injection. [5]
Does PEG-MGF build muscle?
Nobody knows in humans. The natural MGF splice variant rises in muscle for about a day after heavy exercise and, in cell studies, its E domain makes muscle precursor cells multiply. But no human has been given synthetic PEG-MGF in a published study, and the elderly muscle that would benefit most did not even raise its own MGF after exercise in the one human biopsy study. PeptideAgent grades the evidence animal-only. [1] [2] [4]
What are the side effects of PEG-MGF?
There are no human safety data at all. Anecdotal reports mention injection site pain and swelling. Because it belongs to the IGF-1 family, theoretical concerns include stimulating existing tumors and, less likely given its separate receptor, hypoglycemia. None of this has been studied. [1] [3]
How is PEG-MGF taken?
Products sold online are lyophilized vials for subcutaneous or intramuscular injection, and the pegylation is claimed to extend the half life from minutes to hours or days. No human dosing study exists, so any regimen is invented rather than measured. The one animal study of a synthetic E domain peptide was in mice after heart attack, not in muscle building. [3]
How much does PEG-MGF cost?
There is no licensed source and therefore no legitimate price. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. [5]
Is PEG-MGF banned by WADA?
Yes, explicitly. The WADA Prohibited List names mechano growth factors (MGFs) under section S2 (peptide hormones, growth factors, related substances and mimetics), prohibited at all times in and out of competition. Athletes subject to testing should not use it. [6]
PEG-MGF vs IGF-1 LR3: what is the difference?
Both are IGF-1 family research peptides with no human trials and both are WADA prohibited. IGF-1 LR3 is a full length IGF-1 analog that binds the IGF-1 receptor and has strong anabolic effects in rats; PEG-MGF is only the E domain of the MGF splice variant, acts through a different, unidentified receptor, and is thought to expand muscle precursor cells rather than drive growth directly. Neither is lawfully available for human use. [1] [6]
Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.
From the blog
- Peptides for muscle growth, ranked by human evidence
MK-677, sermorelin, tesamorelin, CJC-1295, IGF-1 LR3, and more ranked by human evidence. None is approved for muscle growth, and all ten are banned in tested sport.
- Peptides for tendon recovery, ranked by human evidence
BPC-157, TB-500, GHK-Cu, PEG-MGF, and IGF-1 LR3 ranked by our evidence grades. None has a published human tendon trial. Here is the ranking, the reasoning, and what does have human data.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Yang SY, Goldspink G. Different roles of the IGF-I Ec peptide (MGF) and mature IGF-I in myoblast proliferation and differentiation. FEBS Lett 2002PubMed 12095637, 2002
- [2]Hameed M et al. Expression of IGF-I splice variants in young and old human skeletal muscle after high resistance exercise. J Physiol 2003PubMed 12562960, 2003
- [3]The E-domain region of mechano-growth factor inhibits cellular apoptosis and preserves cardiac function during myocardial infarction. Mol Cell Biochem 2013PubMed 23712705, 2013
- [4]Goldspink G. Mechanical signals, IGF-I gene splicing, and muscle adaptation. Physiology (Bethesda) 2005PubMed 16024511, 2005
- [5]FDA: Bulk drug substances used in compounding under section 503A of the FD&C Act (links to the Category 1, 2, and 3 lists and the bulks list)FDA, 2026
- [6]WADA Prohibited List, section S2 (names mechano growth factors)WADA, 2026
- [7]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2)FDA
- [8]FDA: Compounding inspections, recalls, and other actions (warning letters to compounders)FDA
- [9]FDA warning letters database: July 30, 2019 letter to a 503A pharmacy that compounded BPC-157 acetate outside section 503AFDA, 2019
- [10]FDA Import Alert 66-41: Detention without physical examination of unapproved new drugs promoted in the U.S. (includes peptide entries)FDA
- [11]FDA: Compounding and the FDA, questions and answersFDA
Cite this page
Free to cite and quote with a link. Data is licensed CC BY 4.0 with attribution to PeptideAgent.
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PeptideAgent. (2026, September 22). PEG-MGF: evidence, legality, and access. https://peptideagent.ai/peptides/peg-mgf- HTML link
<a href="https://peptideagent.ai/peptides/peg-mgf">PEG-MGF: evidence, legality, and access</a>, PeptideAgent, updated September 22, 2026.