IGF-1 LR3 — questions, answered plainly.

IGF-1 LR3 is a recombinant analogue of insulin-like growth factor 1 with an N-terminal extension and an arginine substitution at position 3. The modifications reduce binding to IGFBPs (IGF binding proteins), prolonging its activity. It is used as a research reagent — it is not approved for human therapeutic use.

Native IGF-1 binds tightly to IGF binding proteins (IGFBPs) which limit its free fraction. LR3 IGF-1's Arg3 substitution and N-terminal extension reduce IGFBP affinity, leaving more peptide free to bind the IGF-1 receptor in research contexts.

No. IGF-1 LR3 is not approved for human therapeutic use in any jurisdiction. Its primary documented uses are as a cell-culture supplement, a bioproduction reagent, and a research compound in animal-physiology studies.

Lu 2023 (Appl Microbiol Biotechnol, PMID 37261455) reports recombinant production methodology in P. pastoris. Hill 1999 (Domest Anim Endocrinol, PMID 10370861) reports protein-conservation effects in undernourished beef heifers. Jonker 2020 (FASEB J, PMID 32573852) reports cardiomyocyte proliferation and matched coronary growth in fetal sheep.

Yes. Like all IGF-axis agents, LR3 IGF-1 is on the World Anti-Doping Agency prohibited list at all times (S2 — peptide hormones, growth factors). This is separate from its therapeutic-approval status.

The published literature is dominated by bioproduction and animal-physiology research. No PubMed-indexed controlled human clinical trials of IGF-1 LR3 are cited on this profile.