Quick summary
IGF-1 LR3 is an 83-amino acid recombinant analog of IGF-1 engineered to reduce binding protein sequestration by ~1000-fold, extending its half-life to 20-30 hours and making it approximately three times more potent than native IGF-1 in promoting muscle hypertrophy and recovery.
Overview
IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a 83-amino acid recombinant analog of native IGF-1, engineered with a 13-amino acid N-terminal extension and an arginine substitution at position 3. These modifications reduce binding to IGF-binding proteins (IGFBPs) by ~1000-fold and extend half-life to 20–30 hours versus native IGF-1's 12–15 minutes. It is approximately three times more potent than native IGF-1 in anabolic signaling.
Mechanism of action
IGF-1 LR3 binds to the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase, with high affinity. Receptor activation triggers autophosphorylation and downstream signaling through two primary pathways: the PI3K/Akt/mTOR axis, which drives protein synthesis, suppresses protein degradation, and promotes cell survival; and the MAPK/ERK pathway, which stimulates cell proliferation and differentiation. The near-complete bypass of IGFBPs — which normally sequester native IGF-1 in circulation — means systemically administered IGF-1 LR3 is substantially more bioavailable at tissue IGF-1R. Satellite cell activation in skeletal muscle is a key mechanism for hypertrophic adaptation. IGF-1 LR3 also exhibits insulin-like metabolic activity at high concentrations, activating insulin receptors and driving glucose uptake into muscle tissue.
Dosing protocols
| Purpose | Route | Dosage | Frequency | Notes |
|---|---|---|---|---|
| Muscle anabolism / body recomposition research | subcutaneous | 20–50 mcg | once daily, post-workout | Start at 20 mcg/day. Do not exceed 100 mcg/day. Administer post-workout near target muscle groups. 4-week cycles only; extended use risks receptor downregulation and IGF-1R desensitization. Monitor for hypoglycemia — have fast-acting carbohydrates available. |
| Recovery from injury | intramuscular | 20–40 mcg | once daily | Inject into or near the injured muscle. 2–4 week cycles. |
Dosing information is for educational purposes only. Consult a qualified healthcare professional before using any peptide.
Research summary
IGF-1 LR3 is an established research tool in cell biology and metabolic research. In vitro studies consistently demonstrate potent proliferative and anabolic effects in myoblast and fibroblast cell lines. Rodent studies show accelerated muscle hypertrophy, enhanced satellite cell proliferation, and improved recovery from muscle injury. Human pharmacokinetic data from recombinant IGF-1 therapy (mecasermin) provides indirect mechanistic evidence; no controlled human trials specific to IGF-1 LR3 have been published as of 2026. Hypoglycemia risk at higher doses is documented in both animal and human IGF-1 research.[1][2][3][4]
Evidence grading
Each claimed benefit is graded by the strength of available evidence. Grades reflect study quality, not effect size.
Strong = multiple RCTs · Moderate = limited trials or observational · Preliminary = animal or in vitro only · Insufficient = anecdotal or no published data
Side effects
Side effects vary by individual. This is not an exhaustive list. Report unusual symptoms to a healthcare professional.
Common stacks
Peptides commonly paired with IGF-1 LR3 for synergistic effects.
Legal status
Not FDA-approved for human use. Classified as a research chemical. Banned by WADA and most competitive sports organizations under the peptide hormone category. No reclassification review underway as of 2026. Possession for research purposes is generally legal in the US.
Sourcing & access
Research compound
IGF-1 LR3 is classified as a research compound. Regulatory status varies by jurisdiction. Always verify current legal status and source from vendors providing third-party certificates of analysis (COA).
Frequently asked questions
IGF-1 LR3 (Long R3 IGF-1) is a modified version of native IGF-1 with a 13-amino acid N-terminal extension and an arginine substitution at position 3. These changes dramatically reduce binding to IGF-binding proteins, increasing bioavailability and extending half-life from ~15 minutes to 20-30 hours.
IGF-1 LR3 binds the IGF-1 receptor, activating PI3K/Akt/mTOR (driving protein synthesis and cell survival) and MAPK/ERK (stimulating proliferation) pathways. It activates satellite cells in skeletal muscle for hypertrophy and exhibits insulin-like metabolic activity at high concentrations.
Side effects include dose-dependent hypoglycemia (serious), fatigue, jaw pain, headache, water retention, and acromegaly-like symptoms with long-term use. It is not FDA-approved, is banned by WADA, and no controlled human trials specific to IGF-1 LR3 have been published.
Hypoglycemia is a serious dose-dependent risk because IGF-1 LR3 activates insulin receptors at high concentrations, driving glucose uptake into muscle tissue. Users should have fast-acting carbohydrates available and not exceed recommended dosing. Cycles should be limited to 4 weeks.
Research references
- Long R3 insulin-like growth factor-I infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pigPubMed
- Insulin-like growth factor-I analogue, LR(3)IGF-I, ameliorates the loss of body weight but not of skeletal muscle during food restrictionPubMed
- Mechanisms of IGF-1-Mediated Regulation of Skeletal Muscle Hypertrophy and AtrophyReview
- Detection of LongR3-IGF-I, Des(1-3)-IGF-I, and R3-IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposesPubMed