# IGF-1 LR3

> Evidence tier C — Animal data · GH & Growth · reviewed 2026-11-08
> Source page: https://peptidemeta.com/p/igf-1-lr3/

Also known as: Long R3 IGF-1, LR3-IGF-1

## Quick answers

**What is IGF-1 LR3?**

A potent long-acting analog of insulin-like growth factor 1 with an extended half-life due to an arginine substitution. 83-residue IGF-1 analogue (Arg3 substitution plus 13-residue N-terminal extension) with reduced IGF-binding-protein affinity.

**How strong is the evidence for IGF-1 LR3?**

Tier C (animal data) on the peptidemeta evidence scale. Used mainly as a cell-culture reagent and in animal studies; no human trials.

**Is IGF-1 LR3 FDA-approved?**

No. IGF-1 LR3 is not approved by the FDA for any use.

**Is IGF-1 LR3 banned in sport?**

Yes. IGF-1 LR3 is prohibited in sport by the World Anti-Doping Agency under S2 (peptide hormones, growth factors, related substances and mimetics).

**How does IGF-1 LR3 work?**

IGF-1 LR3 is a modified IGF-1 with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension, reducing IGFBP binding and extending its half-life from 12 minutes to 20-30 hours. It activates the IGF-1 receptor tyrosine kinase, stimulating the PI3K/Akt/mTOR pathway for protein synthesis and the Ras/MAPK pathway for cell proliferation.

**What is known about the safety of IGF-1 LR3?**

No formal human clinical trial data for therapeutic use. Potent growth factor with risks including hypoglycemia, organ growth, and theoretical cancer promotion via mTOR/proliferative signaling.

## Key facts

- **Evidence tier:** C (Animal data)
- **FDA:** not approved
- **WADA:** prohibited (S2)
- **Peptide:** yes
- **Routes studied:** Subcutaneous, Intramuscular

## Overview

A potent long-acting analog of insulin-like growth factor 1 with an extended half-life due to an arginine substitution. It drives muscle hypertrophy and nutrient partitioning.

## Mechanism

IGF-1 LR3 is a modified IGF-1 with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension, reducing IGFBP binding and extending its half-life from 12 minutes to 20-30 hours. It activates the IGF-1 receptor tyrosine kinase, stimulating the PI3K/Akt/mTOR pathway for protein synthesis and the Ras/MAPK pathway for cell proliferation.

## Effects reported in research

_Reported outcomes, not promises; see the evidence tier._

- Enhanced muscle protein synthesis
- Improved nutrient partitioning toward muscle
- Promoted hyperplasia (new muscle cell formation)
- Increased nitrogen retention

## Safety & unknowns

No formal human clinical trial data for therapeutic use. Potent growth factor with risks including hypoglycemia, organ growth, and theoretical cancer promotion via mTOR/proliferative signaling. Banned by WADA. Not FDA-approved. Requires careful glucose monitoring.

## Studies

- Jones JI, Clemmons DR. (1995). *Insulin-like growth factors and their binding proteins: biological actions*. Endocrine Reviews. Review. https://pubmed.ncbi.nlm.nih.gov/7758431/
  Foundational review of IGF-1 biology, receptor signaling, and IGFBP interactions relevant to understanding the LR3 modification.

## Status sources

- [PubMed: Long R3 IGF-I](https://pubmed.ncbi.nlm.nih.gov/?term=long+R3+IGF-I)
- [WADA 2026 Prohibited List](https://www.wada-ama.org/en/prohibited-list)

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Educational reference only — not medical advice. No dosing information is published. Tiers rate the strength of published evidence, not effectiveness or safety.