# IGF-1 LR3

> A long-acting modified IGF-1 analog with reduced IGFBP binding and prolonged systemic activity.

- Also known as: Long R3 IGF-1, LR3 IGF-1
- Class: Growth Hormone
- FDA approved: No
- Canonical page: https://www.americanpeptide.com/catalog/igf-1-lr3

## Overview

IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analog of IGF-1 with an arginine substitution at position 3 and a 13-residue N-terminal extension. These changes reduce binding to IGF-binding proteins, extending its half-life and potency versus native IGF-1.

IGF-1 LR3 ("Long R3 IGF-1") is a modified version of insulin-like growth factor 1, engineered for a much longer duration of action. Two changes define it: arginine replaces glutamic acid at position 3, and a 13-amino-acid extension is added to the N-terminus.

Together these reduce the analog’s affinity for IGF-binding proteins — the carriers that normally sequester circulating IGF-1 — so more remains free and active, extending half-life and increasing potency roughly two- to three-fold over native IGF-1 (~9.1 kDa). It is a research compound, widely used in cell culture, and is not FDA-approved; it is also prohibited in sport.

## Mechanism

IGF-1 receptor agonism with reduced IGFBP binding → prolonged systemic anabolic signaling.

## Chemistry

| Property | Value |
| --- | --- |
| CAS number | 946870-92-4 |

## Research areas

Studied in: Muscle hypertrophy, Cell proliferation, GH/IGF-1 axis.

Guides on this site:

- [Growth Hormone & Body Composition](https://www.americanpeptide.com/research-areas/growth-hormone-axis): Secretagogues studied for GH release, IGF-1, and body composition.

## Key research

- Reduced IGFBP binding — the R3 substitution lowers affinity for IGF-binding proteins, leaving more peptide free and active.
- Prolonged potency — systemic, long-acting anabolic signaling roughly two- to three-fold more potent than native IGF-1.
- Cell-culture standard — widely used as a serum-free supplement to promote cell proliferation in bioprocessing.
- Compared to MGF — IGF-1 LR3 is systemic and long-acting (hypertrophy), while MGF is a local, transient splice variant (satellite-cell activation).
- Preclinical / prohibited in sport — not FDA-approved; WADA-banned.

## Storage, handling & synthesis

**Storage.** Lyophilized: store frozen and protected from light. Reconstituted: refrigerate at 2–8 °C and minimize freeze–thaw — a folded, disulfide-bonded protein.

**Handling.** A disulfide-bonded protein sensitive to heat, agitation, and freeze–thaw. Reconstitute gently (swirl, do not shake).

## FAQs

### What is IGF-1 LR3?

IGF-1 LR3 (Long R3 IGF-1) is a modified, long-acting analog of IGF-1 with an arginine-3 substitution and an N-terminal extension that reduce IGF-binding-protein binding and extend its activity.

### Why does the R3 modification matter?

It lowers the analog’s affinity for IGF-binding proteins, so more remains free and active in circulation — extending half-life and increasing potency versus native IGF-1.

### How does it compare to MGF?

IGF-1 LR3 is systemic and long-acting, studied for hypertrophy; MGF is a local, transient IGF-1 splice variant studied for satellite-cell activation. The two are typically sequenced, not combined.

### Is IGF-1 LR3 approved?

No. It is a research compound (also common in cell culture), not FDA-approved, and is prohibited in sport. This page is a research and educational reference.

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Source: AmericanPeptide.com — https://www.americanpeptide.com/catalog/igf-1-lr3
Data license: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Attribution: AmericanPeptide.com.
Research reference only — computational and educational content, not medical advice.