IGF-1 LR3 vs MGF

Side by side

IGF-1 LR3 Low and MGF Low are both marketed as growth factors for muscle, and both trace back to insulin-like growth factor 1 (IGF-1), the hormone through which much of growth hormone's effect is carried out. WADA's 2026 List prohibits both under its growth factors section ¹. The table is read from our encyclopedia entries.

Two very different molecules

IGF-1 LR3 is full-length IGF-1 with one amino acid swapped and a 13-amino-acid extension added to the front. The changes stop it binding the IGF-binding proteins that normally hold IGF-1 in check, which makes it more potent in cell culture and changes how long it lasts in the body ¹. It was developed as a laboratory reagent for growing cells, and is still produced for that purpose; one recent study made it in yeast at gram-per-litre scale for cell culture use ².

MGF, mechano growth factor, is something else. The IGF-1 gene can be read in several ways, and one version, IGF-1Ec, rises in muscle after loading or injury. Its distinctive end piece, the E domain, has been made synthetically as a 24-amino-acid peptide, and that fragment, not a full growth factor, is what laboratories study and sellers market ³. 'PEG-MGF' is the same fragment with a polyethylene glycol chain added.

What IGF-1 LR3 has been shown to do

IGF-1 LR3's studies are in animals. Infused for a week in guinea pigs, it did not change body weight gain, feed efficiency or carcass composition, though some organ weights increased ⁴. Injected in calves, it lowered the animals' own IGF-1 and growth hormone, and lowered blood glucose and insulin ^{5 6}. In rats it increased intestinal glucose uptake ⁷, and in fetal sheep a short infusion lowered fetal insulin by 66% during a glucose clamp ⁸. None of this is a muscle-building result in adult animals, let alone in people.

Product quality is a separate problem. Researchers developing a doping test for IGF-1 analogues found oxidised, lower-quality peptide in black-market products ⁹. According to our entry, no published study has given IGF-1 LR3 to a person ¹.

What MGF has been shown to do

MGF's evidence is thinner still. Applied to cultured human muscle cells from donors of different ages, the synthetic E peptide extended the proliferative lifespan of satellite cells from young donors but not old ones, and increased fibre growth in all cultures ¹⁰. In genetically modified mice, switching on extra MGF in the brain from an early age increased new neurons in the olfactory bulb in old age ¹¹. The human studies measure the gene's expression in patients' tissue: in colorectal tissue, IGF-1Ec expression was higher in cancers and high-grade polyps than in normal colon ¹². That is a reason for caution about a product sold to stimulate the same pathway, not evidence of benefit.

Risks both share

IGF-1 signalling drives cell growth and division, which is why long-term exposure is a concern in any context where abnormal cells could take advantage. IGF-1 also lowers blood sugar, and the animal studies of IGF-1 LR3 show glucose and insulin falling ⁶. Without human studies, nobody knows what doses, if any, are tolerated, how long they last in people or what they do over months. The approved drug in this family, recombinant human IGF-1 sold as mecasermin, is a different molecule given to children with severe primary IGF-1 deficiency under specialist supervision ¹.

How the differences add up (as of October 3, 2026)

IGF-1 LR3 is a potent, long-acting laboratory reagent with animal data and documented black-market quality problems; MGF is a synthetic fragment with cell and mouse data. Neither has been tested in people, neither is approved, and both are banned in sport ¹. Our guide to reading a peptide study explains why a stack of animal studies is not evidence of a human benefit. The IGF-1 growth-factor peptides article adds IGF-1 DES and the low-blood-sugar risk the whole family shares.

Frequently asked questions

What is the difference between IGF-1 LR3 and MGF?

IGF-1 LR3 is a modified full-length IGF-1 that escapes binding proteins and is used as a cell-culture reagent; MGF is a 24-amino-acid synthetic fragment from one splice variant of the IGF-1 gene. Both are sold for muscle growth.

Has IGF-1 LR3 been tested in humans?

No. According to our entry, no published study has given IGF-1 LR3 to a person; its studies are in animals and cells.

Is MGF the same as IGF-1?

No. MGF refers to the E-domain peptide of the IGF-1Ec splice variant, not the full IGF-1 hormone.

Related on Grey Peptides

• IGF-1 LR3
• MGF
• Mecasermin

Sources

1. Grey Peptides dataset records for both compounds (status, half-life and studied doses as sourced on each entry); read October 2, 2026.
2. Lu, Z., et al. (2023). Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris. Appl Microbiol Biotechnol, 107(14), 4543-4551. PMID: 37261455
3. Vassilakos, G., et al. (2014). Biological activity of the e domain of the IGF-1Ec as addressed by synthetic peptides. Hormones (Athens), 13(2), 182-96. PMID: 24776619
4. Conlon, M. A., et al. (1995). Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig. J Endocrinol, 146(2), 247-53. PMID: 7561636
5. Hammon, H., et al. (1997). The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I. Am J Physiol, 273(1 Pt 1), E130-8. PMID: 9252489
6. Hammon, H., et al. (1998). Endocrine and metabolic changes in neonatal calves in response to growth hormone and long-R3-insulin-like growth factor-I administration. Biol Neonate, 73(2), 121-8. PMID: 9483305
7. Garnaut, S. M., et al. (2002). Effects of insulin-like growth factor-I and its analogue, long-R3-IGF-I, on intestinal absorption of 3-O-methyl-D-glucose are less pronounced than gut mucosal growth responses. Growth Factors, 20(1), 17-25. PMID: 11999215
8. White, A., et al. (2023). Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets. J Dev Orig Health Dis, 14(3), 353-361. PMID: 37114757
9. Mongongu, C., et al. (2021). Detection of LongR(3) -IGF-I, Des(1-3)-IGF-I, and R(3) -IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes. Drug Test Anal, 13(7), 1256-1269. PMID: 33587816
10. Kandalla, P. K., et al. (2011). Mechano Growth Factor E peptide (MGF-E), derived from an isoform of IGF-1, activates human muscle progenitor cells and induces an increase in their fusion potential at different ages. Mech Ageing Dev, 132(4), 154-62. PMID: 21354439
11. Tang, J. J., et al. (2017). Mechano growth factor, a splice variant of IGF-1, promotes neurogenesis in the aging mouse brain. Mol Brain, 10(1), 23. PMID: 28683812
12. Alagaratnam, S., et al. (2020). Increased expression of IGF-1Ec with increasing colonic polyp dysplasia and colorectal cancer. J Cancer Res Clin Oncol, 146(11), 2861-2870. PMID: 32772171

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.