IGF-1 LR3

A lab-engineered, longer version of the body's insulin-like growth factor 1. It swaps one amino acid (glutamic acid to arginine at position 3) and adds a 13-residue extension. Its main real-world use is as an ingredient in cell-culture media for biomanufacturing.

IGF-1 acts on the IGF-1 receptor to drive cell growth, protein synthesis and glucose uptake. In blood, natural IGF-1 is mostly held in check by binding proteins. LR3 binds those proteins only weakly, so more stays free to reach the receptor, making it more potent in cell and animal experiments.

No human trials of IGF-1 LR3 were found; the only human-relevant work is an anti-doping urine test. In rats it was anabolic in steroid-treated and diabetic models, increasing body weight and muscle protein synthesis. In atherosclerosis-prone mice it reduced vessel narrowing. In cell culture it increases growth, viability and protein output, outperforming native IGF-1 in serum-free media. Human pharmacokinetics, blood-sugar effects and long-term cancer risk are unknown.

No human safety data exists for LR3. The approved IGF-1 drug lists low blood sugar in 42% of trial subjects, plus anaphylaxis, intracranial hypertension, lymphoid overgrowth and postmarketing cancers, more often at higher exposures. Observational data link higher natural IGF-1 to several cancers.

Not approved for any use; the related approved drug is mecasermin (Increlex) for a rare pediatric IGF-1 deficiency. At 83 amino acids FDA treats it as a biologic, so it cannot be compounded under 503A; it is not on FDA's 2026 compounding lists. WADA prohibits IGF-1 and its analogs at all times under S2. Status as of October 2026.