Educational reference only. Informational material drawn from peer-reviewed literature. Not medical advice and not a recommendation to use, dose, or modify any therapy. Decisions about hormone therapy should be made with a qualified healthcare provider.
Overview
Overview
IGF-1 LR3 is a research peptide with a substantially worse safety profile than native IGF-1. The modifications that make it commercially attractive (longer half-life, higher potency) also amplify every risk associated with IGF-1 use. This compound is not approved for human use anywhere in the world. Long-term safety data does not exist. Use carries meaningful risk of hypoglycemia, organ enlargement, and accelerated tumor growth.
IGF-1 LR3 (Long R3 IGF-1) is a modified version of insulin-like growth factor 1 originally developed for cell culture research. Two modifications distinguish it from native IGF-1: (1) Arginine substitution at position 3 (the "R3"), which reduces binding to IGFBP-3, increasing free/bioavailable IGF-1; (2) N-terminal extension of 13 amino acids (the "Long"), which increases molecular stability and half-life. These changes result in a compound roughly 3x more potent than native IGF-1 with a half-life of 12-15 hours (vs. 10-20 minutes for native IGF-1). LR3 was never developed for human therapeutic use. It exists as a research chemical for studying IGF-1 receptor activity in vitro and was never intended for in vivo human administration.
This entry exists because the compound is widely discussed and used in performance circles. Inclusion is not endorsement.
Forms
Available forms & half-lives
| Form | Approximate half-life |
|---|---|
| Subcutaneous injection (standard) | 12-15 hours |
| Intramuscular injection | 12-15 hours |
What it does
Main effects
- Muscle hypertrophy: direct stimulation of muscle protein synthesis via IGF-1 receptor activation throughout the body, sustained by the 12-15 hour half-life
- Hyperplasia: promotion of new muscle cell formation (theoretical advantage over compounds that only enlarge existing cells)
- Recovery: particularly tendon and ligament healing
- Muscle preservation: anti-catabolic signaling during caloric deficit
- Site-specific growth: a claimed localized effect from local injection; there is limited evidence that IGF-1 acts tissue-selectively, and IGF-1 receptors are expressed across most tissues
What to watch for
Common side effects
- Severe hypoglycemia: 12-15 hour half-life means hypoglycemic potential extends overnight; users have documented severe nocturnal hypoglycemia episodes; blood glucose is the marker that tracks it
- Tumor growth promotion: more potent, longer-duration IGF-1 receptor activation provides prolonged cellular proliferation signaling; any existing precancerous or cancerous cells receive sustained growth stimulation
- Organ enlargement: sustained IGF-1 receptor activation in non-target tissues; reports of cardiac hypertrophy, spleen and kidney enlargement, acromegaly-like features with chronic use
- Receptor downregulation: sustained agonism may cause IGF-1 receptor downregulation in some tissues, potentially blunting natural IGF-1 signaling after discontinuation
- No human safety data: unlike mecasermin (FDA-approved with decades of pediatric use data), LR3 has zero human clinical trial data; everything known about safety comes from anecdotal user reports and animal research
- Quality variability: supply is unregulated, so identity, purity and content are unverified; the peptide also degrades with improper temperature handling
Key facts
Key facts worth knowing
- IGF-1 LR3 is a research peptide, not a pharmaceutical. It was developed for cell culture research to study IGF-1 receptor activity in vitro and was never intended for in vivo human administration. No regulatory authority anywhere in the world has approved LR3 for any human indication. All human use is off-label and without clinical trial safety data.
- The half-life difference is the defining risk multiplier. Native IGF-1 has a free half-life of 10-20 minutes: hypoglycemia is acute and resolves quickly. LR3 has a half-life of 12-15 hours: hypoglycemic potential extends overnight. Users have documented severe nocturnal hypoglycemia. The extended half-life that makes LR3 commercially attractive (less frequent injection) is also what makes severe nocturnal hypoglycemia uniquely dangerous.
- LR3 is approximately 3x more potent than native IGF-1 at the receptor. The arginine substitution at position 3 reduces binding to IGFBP-3 by approximately 1000-fold, increasing free/bioavailable IGF-1 substantially. The N-terminal 13-amino-acid extension increases molecular stability. Together, these modifications mean more IGF-1 receptor activation per dose and for a much longer duration than native IGF-1.
- Organ enlargement is a documented concern with chronic LR3 use. Sustained IGF-1 receptor activation in non-target tissues produces reports of cardiac hypertrophy, spleen and kidney enlargement, and acromegaly-like features (jaw, nose, hands, feet). These changes may be irreversible. Annual echocardiogram and abdominal ultrasound monitoring are recommended for users running repeated LR3 cycles.
- WADA prohibits LR3 at all times under S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics. Athletes subject to anti-doping testing should never use this compound. Confirmed detection means a multi-year competition ban. WADA Prohibited List 2024/2025: S2 Peptide Hormones, Growth Factors, Related Substances and Mimetics.
- Compounds that raise IGF-1 indirectly sit on a different evidence base. GH secretagogues such as MK-677, ipamorelin and CJC-1295 raise IGF-1 through the pituitary, so the elevation is pulsatile and still subject to normal feedback. Native-sequence IGF-1 (mecasermin, Increlex) is an approved drug with decades of clinical data behind it. LR3 does neither: it activates the receptor directly for 12-15 hours, with no human trial data of its own.
- The risks scale with total exposure, not with any single dose. Organ enlargement, acromegaly-like change, receptor downregulation and proliferative signaling are all functions of how much IGF-1 receptor activation has accumulated over time, so repeated exposure compounds them. No exposure ceiling has been established in humans, because no human trials exist to establish one.
- Blood glucose is the marker that tracks LR3's acute risk. IGF-1 receptor signaling shares downstream pathways with the insulin receptor, so LR3 lowers blood glucose, and the 12-15 hour half-life means it can keep doing so for hours. A fasted state, exercise and alcohol all deepen the effect. Hypoglycemia is hardest to recognize when it develops during sleep, and beta-blockers can mask the autonomic warning signs entirely.
Legal status
Legal status
Not FDA-approved for any human use. Sold as a research chemical. Possession generally legal as research chemical in the United States; illegal for sale for human use. Sale for human use is illegal; sale for research use is permitted with appropriate labeling. Restrictions vary by jurisdiction internationally. WADA-prohibited at all times (S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics). Athletes subject to anti-doping testing should never use this compound.