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IGF-1 LR3, also written Long R3 IGF-I or LR3 IGF-I, is a lab-made analog of insulin-like growth factor 1 (IGF-1). It is not FDA-approved for any use in people, and no approved medicine in the United States contains it.
Natural IGF-1 is a hormone made mainly in the liver in response to growth hormone. IGF-1 LR3 adds a 13-amino-acid extension to the start of the IGF-1 chain and swaps the glutamic acid at position 3 for arginine, which is where the R3 in the name comes from.
In the blood, most natural IGF-1 is held by IGF-binding proteins, which limit how much reaches tissues. According to a supplier, the two changes in IGF-1 LR3 reduce its affinity for these binding proteins by more than 1,000-fold, so more of it stays free.
In a 1992 study in rats, IGF-1 LR3 was about 2.5 times as potent as IGF-1, even though it bound the IGF-1 receptor about three times less strongly. The researchers linked the difference to its weak binding to IGF-binding proteins.
IGF-1 LR3 was developed by the Australian company GroPep. Its main established use is industrial. It is sold as a cell culture supplement, an alternative to insulin in serum-free media used to grow cells for biopharmaceutical manufacturing, and suppliers make it in E. coli bacteria for that purpose.
Published studies of IGF-1 LR3 as a potential medicine date mainly from the 1990s and were done in animals, including rats, guinea pigs and sheep. They measured things such as organ weight, gut growth and muscle protein breakdown. In a 1995 guinea pig study, for example, it increased the relative weight of the gut, kidneys, spleen and adrenal glands without increasing overall growth.
We found no published clinical trial of IGF-1 LR3 in people. Its safety in humans has not been established.
Current status: Not FDA-approved.
IGF-1 LR3 has not gone through FDA review for use in people. When a supplier says the ingredient is used in making approved biologic drugs, that refers to its role in growing cells, not to use as a medicine. Products sold online as IGF-1 LR3 are not approved medicines, and the FDA has not reviewed their contents or purity.
It should not be confused with mecasermin (Increlex), a lab-made copy of natural human IGF-1. The FDA approved Increlex in 2005 for growth failure in children aged 2 and older with severe primary IGF-1 deficiency, or with growth hormone gene deletion and neutralizing antibodies to growth hormone.
There is no FDA label for IGF-1 LR3. The label for Increlex shows the risks the FDA highlights for natural IGF-1 therapy. Its warnings include severe low blood sugar that has led to seizures, allergic reactions including anaphylaxis, raised pressure inside the skull, enlarged tonsils and adenoids, a hip problem called slipped capital femoral epiphysis, worsening scoliosis, and cases of cancer in children treated with it. These warnings apply to Increlex; the effects of IGF-1 LR3 in people have not been studied.
The WADA 2026 Prohibited List names insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues under class S2 (peptide hormones, growth factors, related substances and mimetics). They are prohibited at all times, in and out of competition.
Peptide Labs does not sell this compound. This page is general information, not medical advice. We do not supply, prepare or distribute IGF-1 LR3 in any form, and nothing on this page should be read as an offer.
If you have questions about IGF-1 LR3 or a related health concern, talk to a licensed healthcare provider who knows your medical history.
See the full list of compound profiles in the Peptide Guide. Related profiles on the growth hormone axis include CJC-1295 and sermorelin. For a plain-English introduction, read what peptides are.
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