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IGF-1 LR3

Modified IGF-1 analogue with drastically reduced IGFBP binding - longer-circulating and more potent per microgram than native IGF-1.

Research chemicalWADA S2 prohibitedInjectableAnabolic
Key facts
Common routesSC, IM
Half-life20–30 h
Typical range20–50 mcg/day
Summary

IGF-1 LR3 is a synthetic, modified version of Insulin-like Growth Factor 1. An arginine substitution at position 3 plus a 13-amino-acid N-terminal extension cut binding to IGF-binding proteins by >1000x - the LR3 molecule circulates freely instead of being sequestered by IGFBPs.

Result: half-life of 20–30 hours instead of minutes, potency per microgram several-fold higher. Bodybuilding use dominates; acute hypoglycemia and long-term growth-pathway risks are the two main problems.

Mechanism notes
IGF-1 receptor (potentiated)
Binds the IGF-1 receptor with high affinity. Because it doesn't bind IGFBPs, it stays biologically active in the blood far longer than endogenous IGF-1.
PI3K/Akt signalling
Strongly activates PI3K/Akt - the core driver of protein synthesis and inhibitor of muscle proteolysis.
Hyperplasia (satellite cells)
Stimulates satellite-cell proliferation and differentiation - theoretically forming new muscle fibres rather than just enlarging existing ones.
Dosing patterns
Blast protocol (4 weeks max)
30–50 mcg daily SC post-workout, ≀4 weeks, then 4 weeks washout. Standard community discipline against receptor downregulation and growth-pathway accumulation.
Post-injection carbs
30–50 g fast carbs immediately post-injection. Non-negotiable - the hypoglycemia response can be acute.
Evidence snapshot
Mechanism cleanly characterised in vitro and in animal models (Tomas et al. 1991). LR3-specific human trials don't exist - clinical IGF-1 data is on rhIGF-1 (Mecasermin), a different molecule.
Animal models
Higher potency than rhIGF-1 in rats; visceral organ hypertrophy ("bubble gut") at chronic high doses.
Human data
No published trials specific to LR3. Risk extrapolated from IGF-1 receptor pharmacology and native IGF-1 epidemiology.
Safety considerations
Acute hypoglycemia is the immediate threat; chronic supraphysiologic IGF-1 is the long-term question. Use demands strict cycle discipline and glucose management.
Common cautions
  • Acute hypoglycemia if post-injection carbs are skipped
  • Visceral organ hypertrophy (bubble gut) at chronic high dose
  • Theoretical tumour-promotion risk in pre-existing malignancies
  • EXTREME DANGER: stacking with exogenous insulin can be fatal
IGF-1 LR3