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IGF-1 LR3: quick citable summary
IGF-1 LR3 is listed by PeptaHub as a muscle & growth peptide with a research only legal-status classification. The page summarizes mechanism, research context, common routes, safety notes, and references for writers and AI answer engines.
PeptaHub. “IGF-1 LR3: Mechanism, Research Context, Safety.” peptahub.com, 2026. https://peptahub.com/peptides/igf-1-lr3. Licensed CC BY 4.0.
License: Creative Commons Attribution 4.0 International. Link back to https://peptahub.com/peptides/igf-1-lr3.
What is IGF-1 LR3?
IGF-1 LR3 is an 83-amino acid recombinant analog of IGF-1 engineered to escape IGF-binding-protein sequestration, which extends its circulating half-life well beyond native IGF-1. It is a laboratory research reagent: no controlled human trial of IGF-1 LR3 has been published.
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 greatly reduce binding to IGF-binding proteins (IGFBPs) and extend its circulating half-life well beyond that of native IGF-1, which is cleared within minutes when unbound. The specific half-life and potency multiples quoted in community sources are not supported by any published human pharmacokinetic study.
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.
Reported study ranges
| Purpose | Route | Reported range | Frequency | Notes |
|---|---|---|---|---|
| Muscle anabolism / body recomposition research | subcutaneous | 20–50 mcg | once daily, post-workout | These are community-reported ranges with no clinical trial behind them: no human dosing study of IGF-1 LR3 has been published. Hypoglycemia is a serious documented risk of the IGF-1 class. |
| Recovery from injury | intramuscular | 20–40 mcg | once daily | Community-reported practice only. No human study supports local injection of IGF-1 LR3 for injury recovery. |
Reported ranges are for research context only. Consult a qualified healthcare professional before using any peptide.
Convert IGF-1 LR3 research-range units
Need to convert mg to mcg, dose volume, or U-100 syringe units? The IGF-1 LR3 dose calculator is preloaded with these ranges, or use the general dose unit converter.
Research summary
IGF-1 LR3 is an established research reagent in cell biology and metabolic research. The animal data are narrower than commonly assumed: infusion in guinea pigs stimulated organ growth while suppressing endogenous IGF-I, IGF-II and IGFBPs (Conlon, J Endocrinol 1995), and in food-restricted rats LR3-IGF-I limited body weight loss but did not preserve skeletal muscle (Tomas, Growth Horm IGF Res 2001). The muscle hypertrophy rationale rests on general IGF-1/PI3K/Akt/mTOR signalling rather than on LR3-specific in vivo hypertrophy trials. No controlled human trial of IGF-1 LR3 has been published as of 2026. Hypoglycemia is a documented class risk of IGF-1 therapy.[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 sharply reduce binding to IGF-binding proteins, increasing free bioavailability and substantially extending the circulating half-life relative to native IGF-1. No published human pharmacokinetic study of IGF-1 LR3 pins down the exact figure.
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 (IGF-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