How IGF-1 LR3 works
An unapproved growth signal with no human trials found.
Also called: Long R3 IGF-I, Long Arg3 IGF-1, LR3-IGF-1, Long-[Arg3]IGF-I.
IGF-1 and analogues · Modified IGF-1 receptor agonist · Evidence: Animal studies only.
LR3 activates the IGF-1 receptor, a signal for cells to grow and use nutrients. Its changes reduce binding to proteins that normally control IGF-1. That changes its activity in laboratory models. The size and duration of its effects in people are unknown.
- IGF-1 receptor: Activates growth and survival signals in cells.
- IGF-binding proteins: Binds less strongly than native IGF-1; activity cannot be converted dose-for-dose.
Half-life: Unknown in humans. The often-repeated 20–30-hour value is not confirmed by a human LR3 PK study.
Related to IGF-1 LR3
- Mecasermin: Prescription IGF-1 approved for rare childhood growth failure; low blood sugar is a major risk.
- Retatrutide: An experimental weekly injection with phase 3 weight-loss results.
- Somatropin: Prescription human growth hormone, with no proven anti-aging benefit.
Sources
- 21 CFR 216.23 — Bulk drug substances that can be used to compound drug products in accordance with section 503A of the Federal Food, Drug, and Cosmetic Act., Office of the Federal Register · eCFR · 2026
- 503B Bulk Drug Substances List, FDA · FDA · 2026
- Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act, FDA · FDA · 2026
- Bulk Drug Substances Used in Compounding Under Section 503A of the FD&C Act, FDA · FDA · 2026
- Cellulitis, NHS · NHS · 2026
- The 2026 Prohibited List, World Anti-Doping Agency · WADA · 2026
- Therapeutic Goods (Poisons Standard—October 2026) Instrument 2026, Australian Government · Australian Government · 2026
- INCRELEX (mecasermin) injection, for subcutaneous use, U.S. Food and Drug Administration · FDA · 2025
- Anaphylaxis, NHS · NHS · 2023
- Low blood sugar (hypoglycaemia), NHS · 2023
- Tailor Made Compounding LLC - 594743 - 04/01/2020, FDA · FDA · 2020
- Increlex, European Medicines Agency
- Increlex, INN-mecasermin, European Medicines Agency
- Know When to Go to the ER, American College of Emergency Physicians · American College of Emergency Physicians
- Mecasermin (Increlex▼): risk of benign and malignant neoplasia, MHRA
Sources checked: 2026-10-18.
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