IGF-1 LR3

What it is

IGF-1 LR3, or Long R3 IGF-1, is a laboratory-made analogue of insulin-like growth factor 1 (IGF-1) rather than the naturally occurring hormone S3. It differs from native IGF-1 by a substitution of arginine for glutamic acid at position 3 and a 13-amino-acid extension on the N-terminus, changes that give it very low affinity for the insulin-like growth-factor-binding proteins (IGFBPs) S3. Because it evades those carrier proteins, it is described as more potent and longer-acting than native IGF-1 in laboratory settings S3S4. In legitimate use it is sold as a research protein and cell-culture media supplement for growing cells, not as a therapeutic S5.

Marketed as

In gray-market and "research chemical" channels, IGF-1 LR3 is promoted for muscle growth and body composition on the basis of IGF-1's role in tissue growth S3. These marketing claims are not backed by controlled human trials and sit outside any approved medical use S3S4.

Regulatory status (US)

IGF-1 LR3 is not approved by the FDA as a medicine and is distributed as a research-use-only reagent, not for human consumption S5. It should not be confused with mecasermin (brand name Increlex), a recombinant human IGF-1 that the FDA first approved in 2005 S2. Mecasermin is a different product with a narrow indication: "the treatment of growth failure in pediatric patients 2 years of age and older with severe primary IGF-1 deficiency or with growth hormone (GH) gene deletion who have developed neutralizing antibodies to GH" S2. That approval does not extend to IGF-1 LR3 or to muscle-building use S2.

Around the world

IGF-1 and its analogues are treated internationally as growth factors falling under anti-doping controls rather than as consumer products S1. Reputable suppliers globally list Long R3 IGF-1 as a research and bioprocessing reagent, consistent with its status as a lab tool rather than an approved drug in major markets S5.

Evidence

The scientific record for IGF-1 LR3 is preclinical and biochemical. Animal-infusion studies of IGF-I analogues that bind poorly to IGF-binding proteins report that their greater potency relative to native IGF-I is maintained even when given by injection S4. This work characterizes how the molecule behaves in cells and animals; it does not establish safety or efficacy for muscle growth in people S4S3.

Anti-doping

IGF-1 and its analogues are prohibited in sport at all times under the World Anti-Doping Agency (WADA) Prohibited List, within Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) S1. The 2026 List names "insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues" among prohibited growth factors, a wording that captures modified variants such as IGF-1 LR3 S1. Substances in this class are non-specified substances prohibited in and out of competition S1.

Safety

Because IGF-1 LR3 has no approved human use, no regulatory safety review, and no established quality standard, its risk profile in people is not defined by any regulator S3S5. Products sold outside a pharmaceutical supply chain are not verified for identity, purity, or sterility S5. Anyone seeking a legitimate IGF-1 medicine should look to an FDA-approved product used under medical supervision, not a research chemical S2.

What's changing

The WADA Prohibited List is reissued annually, and IGF-1 and its analogues have remained within the S2 growth-factor category in the current 2026 edition S1. The broader picture is stable: IGF-1 LR3 continues to be a lab and cell-culture reagent without an approved-medicine pathway, while approved recombinant IGF-1 therapy remains limited to the narrow mecasermin indication S2S5.