Growth Factor Investigational

IGF-1 LR3

Also known as: Long R3 IGF-1, Long Arg3 IGF-1, Mecasermin (related)

A long-acting IGF-1 analog with reduced binding protein affinity — one of the most potent anabolic peptides, capable of promoting both muscle hypertrophy and hyperplasia.

Popularity B+
Class Growth Factor (Modified IGF-1)
Half-Life 20-30 hours
Form Lyophilized powder
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IGF-1 LR3 C400H625N111O115S9
Research-Backed User Reports Sourced Updated Mar 2026
// Overview

What is IGF-1 LR3?

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified version of the naturally occurring IGF-1 protein. The “Long R3” modification involves the substitution of Arg for Glu at position 3 and the addition of a 13 amino acid N-terminal extension, which dramatically reduces binding to IGF binding proteins (IGFBPs).

This reduced IGFBP binding means that IGF-1 LR3 has a much longer half-life (20-30 hours vs 12-15 minutes for native IGF-1) and significantly greater bioavailability and potency. While native IGF-1 is rapidly bound and inactivated by IGFBPs in the bloodstream, LR3 remains free and active for extended periods.

IGF-1 LR3 is one of the most potent anabolic peptides available, capable of promoting both muscle hypertrophy (increasing cell size) and hyperplasia (increasing cell number). It also has significant effects on fat metabolism, recovery, and anti-aging — but its potency demands respect and careful dosing.

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// How It Works

How IGF-1 LR3 Works

IGF-1 LR3 exerts potent anabolic effects through IGF-1 receptor signaling:

  1. IGF-1R activation — Binds to IGF-1 receptors on muscle, bone, and other tissues, activating the PI3K/Akt/mTOR signaling cascade — the master anabolic pathway for protein synthesis.
  2. Reduced IGFBP binding — The LR3 modifications prevent most IGFBP binding, keeping the peptide free and active 100-300x longer than native IGF-1.
  3. Muscle hyperplasia — Unlike most anabolics that only increase cell size (hypertrophy), IGF-1 LR3 can stimulate satellite cell differentiation and fusion, creating entirely new muscle fibers.
  4. Anti-catabolic — Inhibits muscle protein breakdown through Akt-mediated suppression of FOXO transcription factors and the ubiquitin-proteasome pathway.
  5. Nutrient partitioning — Shuttles nutrients preferentially toward muscle tissue and away from fat storage, improving body composition.
// Dosage Protocols

Dosage Information (User-Reported)

Disclaimer: Dosage information is compiled from user reports and published research. This is not medical advice. Consult a healthcare professional before use.
Level Dose Frequency Duration
Starter 20-40 mcg Once daily (post-workout) 4-6 weeks
Standard 40-80 mcg Once daily 4-6 weeks
Advanced 80-120 mcg Once daily (bilateral IM) 4-6 weeks max

What to Expect

Week 1-2

Pump during workouts intensifies. Mild hypoglycemia possible (eat carbs around injection). Recovery between sessions improving.

Week 3-4

Visible muscle fullness. Significant strength gains in the gym. Fat loss may be apparent. Enhanced pumps persist.

Week 5-6

Peak muscle growth effects. Notable body recomposition. IGF-1 LR3 cycles are typically kept short (4-6 weeks) to prevent desensitization.

Post-Cycle

Gains are generally well-retained with continued training. 4-6 week break recommended before repeat cycles.

Common Stacks

Ipamorelin + CJC-1295

GH + IGF-1 Axis

Exogenous IGF-1 combined with stimulated natural GH release for maximum growth axis activation

BPC-157

Recovery Support

Supports tissue repair for the increased training intensity that IGF-1 LR3 enables

Insulin (Advanced)

Synergistic Anabolism

Insulin + IGF-1 is extremely potent but carries serious hypoglycemia risk — advanced users only with medical supervision

// Preparation

Reconstitution & Storage

Reconstitute with bacteriostatic water or 0.6% acetic acid solution. For a 1mg vial, add 1mL for 1mg/mL (100mcg per 0.1mL).

Inject water slowly. Do not shake — extremely fragile protein. Swirl very gently.

Refrigerate immediately. Use within 28 days. Handle with care — IGF-1 LR3 is sensitive to temperature and agitation.

Storage: Lyophilized: -20°C. Reconstituted: 2-8°C, use within 28 days. Avoid freeze-thaw cycles.

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// Safety Profile

Side Effects & Safety

Potential Side Effects

  • ! Hypoglycemia (can be severe — always have carbs available)
  • ! Joint pain and water retention
  • ! Jaw/hand growth with prolonged use (acromegaly-like)
  • ! Intestinal growth (GI discomfort)
  • ! Tumor growth risk (theoretical — IGF-1 is mitogenic)
  • ! Headache
  • ! Lethargy

Contraindications

  • ⚠ Active or history of malignancy (IGF-1 promotes cell proliferation)
  • ⚠ Pregnancy or breastfeeding
  • ⚠ Diabetes (severe hypoglycemia risk)
  • ⚠ Children and adolescents (growth plate implications)
  • ⚠ Organ hypertrophy concerns

Legal & Regulatory Status

Not FDA-approved (Mecasermin/Increlex, a related recombinant IGF-1, is FDA-approved for growth failure). Banned by WADA. Available as a research peptide. Not a controlled substance but closely monitored.

// Research

Published Research

// Where to Buy

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// Related Compounds

Other Growth Factor Guides

Cagrilintide

A long-acting amylin analog that amplifies weight loss when paired with semaglutide — the amylin component of CagriSema's…

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BPC-157 Arginate (Oral)

The oral form of BPC-157 — gastric-acid stable and designed for direct GI tract healing. No injections needed…

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TB-500 Fragment

A concentrated fragment of Thymosin Beta-4 focused on the core actin-binding domain — smaller molecule, targeted tissue repair.

Read Guide →

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This content is for informational and educational purposes only. IGF-1 LR3 is sold for research purposes. Never Natty does not condone or encourage the use of any substance in violation of any laws. Consult a healthcare professional before using any compound discussed on this site.