Which is better, IGF-1 LR3 or PEG-MGF?
This is a comparison of two unproven research chemicals with no lawful human use, so the verdict is about which is better documented, not which to use. Both are graded animal only. IGF-1 LR3 has in vivo rat data on potency and anabolic effect and a known class safety profile from the approved IGF-1 drug mecasermin, including hypoglycemia and a contraindication in cancer. PEG-MGF has only cell culture and mouse cardiac data on the unpegylated E domain peptide, and its 503A nomination was withdrawn. Neither can lawfully be compounded or sold for human use. [1] [2] [3] [4] [5] [6]
How do IGF-1 LR3 and PEG-MGF compare?
| Dimension | IGF-1 LR3Favored | PEG-MGF |
|---|---|---|
| What it is [2] [4] | Recombinant 83 amino acid IGF-1 analog with a 13 amino acid N-terminal extension and arginine at position 3, engineered in 1992 to escape IGF binding proteins. | Pegylated synthetic 24 amino acid peptide copying the E domain of mechano growth factor, a muscle splice variant of IGF-1 (IGF-1Ec). |
| Mechanism [2] [4] | Activates the IGF-1 receptor (and binds the insulin receptor); binds IGF binding proteins poorly, so more stays free and active. | The E domain appears to activate muscle satellite cells and increase myoblast proliferation through a receptor other than the IGF-1 receptor. |
| Animal evidence [1] [4] [5] | In dexamethasone treated rats, about 2.5 fold more potent than IGF-1 on body weight and nitrogen retention, with less muscle protein breakdown and up to 45% more gut weight. | In myoblast culture the E domain increased proliferation and blocked differentiation; in mice a synthetic E domain peptide preserved heart function after infarction. The pegylated form has no published data. |
| Human evidence [3] [7] | No human study of LR3. Class data come from mecasermin, approved native IGF-1 for severe primary IGF-1 deficiency in children. | No human study of any synthetic MGF peptide. Biopsies show natural MGF mRNA rises after resistance exercise in young but not older adults. |
| Expected safety risks [3] [8] | Hypoglycemia (the most common mecasermin adverse effect, likely stronger with LR3), tonsillar hypertrophy, intracranial hypertension, and a cancer contraindication by class. | No human safety data of any kind; theoretical tumor growth concern shared with IGF-1 family peptides. |
| FDA and compounding status [6] | Never nominated or reviewed. Not a component of an approved drug and not on the 503A bulks list, so it cannot lawfully be compounded. | Nominated and placed in 503A Category 2, then withdrawn; no longer in Category 2 but not on the bulks list, with no active nomination. Cannot lawfully be compounded. |
| WADA status [9] [10] | Prohibited at all times under S2 (IGF-1 and its analogues). | Prohibited at all times under S2 (mechano growth factors are named). |
| Original intended use [2] [8] | Cell culture reagent designed to boost growth of cultured cells. | Research tool based on a hypothesized local muscle repair factor. |
Evidence grade and regulatory status
Pulled from each peptide’s own record, so it stays in step with the peptide pages.
| Attribute | IGF-1 LR3 | PEG-MGF |
|---|---|---|
| Class | Recombinant 83 amino acid analog of human IGF-1 with a 13 amino acid N-terminal extension and arginine substituted for glutamate at position 3, engineered in 1992 to escape IGF binding proteins | 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 |
| What it is | Lab research version of the growth factor IGF-1, 2 to 3 times more potent than IGF-1 in rats; no human study, not FDA approved, banned by WADA under S2. | PEG-coated fragment of a muscle form of the growth factor IGF-1: cell and mouse data only, no human trial of the peptide, and named on WADA's banned list. |
| Evidence | Evidence: Animal-only evidence | Evidence: Animal-only evidence |
| FDA status | Regulatory: Unscheduled | Regulatory: Removed from Category 2 (Apr 2026) |
| Compounding | Never submitted to or reviewed by FDA for human use. IGF-1 LR3 is not a component of an approved drug (mecasermin is native IGF-1, a different molecule), has no USP monograph, and has not been placed on the 503A bulks list, so it cannot lawfully be compounded by 503A pharmacies or 503B outsourcing facilities. It is sold as a cell culture reagent and research chemical, which is not lawful for human use. | 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 | WADA: WADA prohibited | WADA: WADA prohibited |
| Routes | Subcutaneous or intramuscular injection (as sold), Continuous subcutaneous infusion (rat studies), Cell culture reagent (its intended use) | Subcutaneous or intramuscular injection (as sold), Intraperitoneal or intravenous (mouse study) |
| 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. | Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. |
| Last verified |
Has IGF-1 LR3 been tested directly against PEG-MGF?
No published trial has compared IGF-1 LR3 and PEG-MGF directly. The dimensions above come from separate studies and labels, and cross-trial comparisons are less reliable than a direct trial.
What do IGF-1 LR3 and PEG-MGF cost?
| Dimension | IGF-1 LR3 | PEG-MGF |
|---|---|---|
| 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. | Not available through licensed channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. |
| Price detail | Price index in progress | Price index in progress |
Where a price index exists, the range is the cash price per month across branded, compounded, and telehealth channels, without insurance. The cost pages give each channel separately with its sources. Otherwise the typical cost from the peptide record is shown. Legal access depends on your state: see peptide legality by state.
Frequently asked questions
Can I get IGF-1 LR3 or PEG-MGF from a doctor?
No lawful US channel exists for either. IGF-1 LR3 was never nominated for compounding, and the PEG-MGF nomination was withdrawn, so neither is on the 503A bulks list. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. [6]
Is IGF-1 LR3 the same as the approved IGF-1 drug?
No. The approved drug, mecasermin, is native IGF-1 for children with severe primary IGF-1 deficiency. IGF-1 LR3 is a modified analog that escapes binding proteins and was about 2.5 fold more anabolic than IGF-1 in rats, which is also why its hypoglycemia risk is expected to be higher. [1] [3]
Does PEG-MGF build muscle in humans?
There is no evidence it does. No human study has given PEG-MGF or any synthetic MGF peptide to people. The human data show only that the body's own MGF gene expression rises after heavy resistance exercise in young adults. [7] [8]
Are they banned in sport?
Yes. IGF-1 analogues and mechano growth factors are both prohibited at all times under S2 of the WADA Prohibited List. [9] [10]
What is the biggest known risk?
For IGF-1 LR3, hypoglycemia, the most common adverse effect of approved IGF-1, plus a class contraindication in active or suspected cancer. For PEG-MGF the risks are simply unknown because no human safety data exist. [3] [4]
Conditions studied
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.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Tomas FM et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J 1992PubMed 1371669, 1992
- [2]Francis GL et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol 1992PubMed 1378742, 1992
- [3]FDA prescribing information for Increlex (mecasermin) injection, via DailyMedFDA, 2024
- [4]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
- [5]The E-domain region of mechano-growth factor inhibits cellular apoptosis and preserves cardiac function during myocardial infarction. Mol Cell Biochem 2013PubMed 23712705, 2013
- [6]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
- [7]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
- [8]Goldspink G. Mechanical signals, IGF-I gene splicing, and muscle adaptation. Physiology (Bethesda) 2005PubMed 16024511, 2005
- [9]WADA Prohibited List, section S2 (names IGF-1 and its analogues)WADA, 2026
- [10]WADA Prohibited List, section S2 (names mechano growth factors)WADA, 2026
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PeptideAgent. (2026, September 22). IGF-1 LR3 vs PEG-MGF: evidence, cost, and legality. https://peptideagent.ai/compare/igf-1-lr3-vs-peg-mgf- HTML link
<a href="https://peptideagent.ai/compare/igf-1-lr3-vs-peg-mgf">IGF-1 LR3 vs PEG-MGF: evidence, cost, and legality</a>, PeptideAgent, updated September 22, 2026.