Is IGF-1 LR3 the same as prescription IGF-1?

No. Prescription IGF-1 (mecasermin) is approved for severe IGF-1 deficiency. IGF-1 LR3 is an unapproved analog sold as a research chemical.

Does it build muscle in humans?

There are no human RCTs showing this. Anabolic effects are extrapolated from cell and animal studies.

What are the cancer concerns?

IGF-1 is a growth factor; elevated circulating IGF-1 has been associated with cancer risk in epidemiology. Direct causality in peptide users is unstudied but mechanistically plausible.

growth

IGF-1 LR3

IGF-1 LR3 is a synthetic analog of insulin-like growth factor 1 with reduced binding to IGF-binding proteins and a longer half-life. It is marketed for muscle growth but has no approved medical use and no human RCT evidence supporting safety or efficacy.

Ian Gauntt, RN BSN1 min readPreclinical

Aliases: Long arginine 3-IGF-1, IGF-1 long R3

Educational content only — this is not medical advice. Nothing here is a recommendation to buy, obtain, or use IGF-1 LR3. Talk to a licensed clinician before making health decisions.

What it is

IGF-1 LR3 is a 83-amino-acid peptide analog of human IGF-1 with an arginine substitution at position 3 and an N-terminal extension of 13 amino acids. These modifications reduce binding to IGF-binding proteins and prolong half-life. It is promoted for anabolic and recovery effects but is not a pharmaceutical product.

What the evidence shows

Evidence is limited to cell-culture and animal studies. In vitro, IGF-1 LR3 potently activates the IGF-1 receptor and stimulates muscle-cell proliferation and protein synthesis. No published human randomized controlled trial has evaluated its effects on muscle, fat, or recovery in people.

Risks & unknowns

IGF-1 signaling is linked to cell growth, proliferation, and cancer risk in epidemiological and animal studies. Exogenous IGF-1 can cause hypoglycemia, fluid retention, organomegaly, acromegaly-like features, and insulin resistance. Unregulated injectable products add infection, contamination, and dosing errors to those risks.

Legal / regulatory status

IGF-1 LR3 is not FDA-approved. It is prohibited by WADA under S2 at all times. Marketing it for human use is illegal.

FAQ

Is IGF-1 LR3 the same as prescription IGF-1?: No. Prescription IGF-1 (mecasermin) is approved for severe IGF-1 deficiency. IGF-1 LR3 is an unapproved analog sold as a research chemical.
Does it build muscle in humans?: There are no human RCTs showing this. Anabolic effects are extrapolated from cell and animal studies.
What are the cancer concerns?: IGF-1 is a growth factor; elevated circulating IGF-1 has been associated with cancer risk in epidemiology. Direct causality in peptide users is unstudied but mechanistically plausible.

References

IGF-1 LR3: binding protein resistance and bioactivity (J Biol Chem, 1993)preclinical
IGF-1 and muscle: preclinical evidence (J Endocrinol, 2016)review
WADA Prohibited Listregulatory