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Growth Factors & IGF

IGF-1 LR3

Also known as Long R3 IGF-1 · Long Arg3 IGF-1 · Insulin-like Growth Factor-1 Long R3

PreliminarySubcutaneous injectionIntramuscular injectionIn vitro / cell-culture application (research settings)Not approved by the FDA for human use and not lawfully marketed as a drug or dietary supplement; it is sold only as a research chemical labeled "for research use, not for human consumption." It is not a recognized compounding candidate — there is no FDA-approved IGF-1 LR3 product, and it does not appear on the FDA's 503A or 503B bulk-substance lists eligible for pharmacy compounding (a status reinforced by the FDA's ongoing tightening of peptide bulks-list eligibility). It is not a DEA-scheduled controlled substance. For athletes, the World Anti-Doping Agency (WADA) prohibits IGF-1 and its analogs, including IGF-1 LR3, under Section S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics) at all times, both in and out of competition.

IGF-1 LR3 is a synthetic, structurally modified analog of human insulin-like growth factor 1 (IGF-1), comprising 83 amino acids versus the native protein's 70, with the native glutamate at position 3 replaced by arginine (the source of the 'Arg3'/'R3' name) and a 13-amino-acid N-terminal extension. These modifications sharply reduce its binding to IGF-binding proteins (IGFBPs), which normally sequester native IGF-1, giving the analog greater free bioavailability and a substantially longer reported half-life (commonly cited around 20-30 hours). Mechanistically it acts as an agonist of the IGF-1 receptor (IGF1R), driving downstream signaling associated with cell growth, proliferation, and activation of muscle satellite cells. The bulk of available data comes from in vitro cell-culture work and animal models, where its extended activity makes it a widely used laboratory tool; rigorous human clinical evidence is lacking and it is not an approved therapeutic. As such, statements about its effects in people remain largely extrapolated from preclinical research.

Studied / used for

  • Investigated in laboratory research for activation and proliferation of muscle satellite cells and muscle-cell biology
  • Studied in cell-culture systems as a sustained IGF-1 receptor agonist for tissue and cellular growth signaling
  • Investigated in animal models for effects on lean-tissue and metabolic IGF-1 pathways
  • Explored preclinically for cellular repair and regeneration signaling pathways

Commonly reported side effects

  • Hypoglycemia and other insulin-like metabolic effects commonly reported, given its IGF-1 receptor activity and extended duration
  • Injection-site reactions such as redness or pain commonly reported with parenteral use
  • Edema and water retention commonly reported
  • Reports of concern regarding off-target tissue or organ growth associated with sustained IGF-1 receptor signaling
Preliminary. Mostly early or animal studies. This reflects the strength of the research base, not effectiveness or a recommendation.

Not medical advice.

This is an educational reference. Peptalk does not recommend, prescribe, endorse, or rate any compound, and provides no dosing information. Do not start, stop, or change any peptide, hormone, supplement, or therapy based on this page. All clinical decisions must be made with your licensed healthcare provider.

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