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The Peptide Effect
preclinicalMuscle Growth & Recovery

IGF-1 LR3

Also known as: Long R3 IGF-1, Insulin-like Growth Factor 1 Long R3, Long Arginine 3-IGF-1, LR3-IGF-1

IGF-1 LR3 is a modified, highly potent analog of Insulin-like Growth Factor 1 (IGF-1) engineered for extended biological activity. With an arginine substitution at position 3 and 13 additional amino acids at the N-terminus, it resists binding by IGF binding proteins, resulting in 2–3x greater potency than native IGF-1. It is one of the most powerful anabolic peptides studied for muscle hypertrophy and cell proliferation.

Key Facts

Mechanism
IGF-1 LR3 is a synthetic analog of IGF-1 featuring an arginine substitution at position 3 and a 13-amino-acid extension at the N-terminus. These structural modifications drastically reduce its affinity for IGF binding proteins (IGFBPs), which normally sequester and deactivate circulating IGF-1. The result is a peptide that remains bioactive far longer than native IGF-1. It activates the IGF-1 receptor (IGF-1R), triggering the PI3K/Akt and MAPK/ERK signaling cascades. This promotes protein synthesis, cell proliferation, satellite cell activation, glucose uptake into skeletal muscle (independent of insulin), and inhibition of apoptosis. Unlike growth hormone, IGF-1 LR3 acts directly on target tissues without requiring hepatic conversion.
Research Status
preclinical
Half-Life
~20–30 hours (significantly longer than native IGF-1 at ~12–15 minutes)
Molecular Formula
C₄₀₀H₆₂₅N₁₁₁O₁₁₅S₉
Primary Use
Muscle Growth & Recovery
Table of Contents

Benefits

  • Potent anabolic effect — promotes skeletal muscle hypertrophy through PI3K/Akt-mediated protein synthesismoderate
  • Enhanced post-exercise recovery and reduced muscle damage markersmoderate
  • Promotes muscle hyperplasia (new muscle cell formation via satellite cell activation), not just hypertrophy of existing fiberspreliminary
  • Improved nutrient partitioning — directs glucose and amino acids preferentially toward muscle tissue over fat storagepreliminary
  • Anti-catabolic properties — inhibits muscle protein breakdown during caloric deficitpreliminary

Dosage Protocols

RouteDosage RangeFrequencyNotes
Subcutaneous injection20–50 mcgOnce dailyInjected bilaterally into target muscles post-workout. Typical cycle length is 4–6 weeks. Start at the low end (20 mcg) to assess hypoglycemic response. Always consume carbohydrates within 15 minutes of injection.
Intramuscular injection20–50 mcgOnce dailyBilateral IM injections in target muscle groups (e.g., split dose between left and right quads). Often preferred for site-specific growth. Same cycle length: 4–6 weeks on, 4–6 weeks off.
Subcutaneous injection (advanced)50–100 mcgOnce dailyHigher doses used by advanced users. Significantly increases hypoglycemia risk. Must be paired with timed carbohydrate intake. Not recommended without prior experience at lower doses.

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Hypoglycemia — IGF-1 LR3 drives glucose into muscle cells, which can cause dangerously low blood sugar. Always have fast-acting carbohydrates on hand during useserious
  • Visceral and organ growth (intestinal, cardiac) with chronic or high-dose use — commonly referred to as "gut growth" or "GH gut"serious
  • Increased theoretical cancer risk — chronic IGF-1 elevation is epidemiologically associated with higher rates of colorectal, breast, and prostate cancers due to sustained cell proliferation signalingserious
  • Joint pain, swelling, or carpal tunnel-like symptomscommon
  • Headache and general malaise, especially during initial usecommon

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Frequently Asked Questions

What is the difference between IGF-1 LR3 and HGH?
HGH (Human Growth Hormone) stimulates the liver to produce IGF-1 as an intermediary. IGF-1 LR3 bypasses this step entirely, acting directly on IGF-1 receptors in muscle and other tissues. HGH has broader systemic effects (fat loss, sleep, skin), while IGF-1 LR3 is more targeted toward anabolic muscle growth and cell proliferation. They work through related but distinct pathways, and some advanced protocols use both together.
How dangerous is the hypoglycemia risk with IGF-1 LR3?
The hypoglycemia risk is significant and should not be underestimated. IGF-1 LR3 drives glucose into muscle cells much like insulin. Symptoms include shakiness, sweating, confusion, dizziness, and in severe cases, loss of consciousness. Users should always have fast-acting carbohydrates (glucose tablets, juice, candy) immediately available and should consume a carbohydrate-rich meal within 15 minutes of injection. Never inject before sleep.
Does injecting IGF-1 LR3 into specific muscles cause localized growth?
There is anecdotal evidence supporting site-specific muscle growth with intramuscular injection of IGF-1 LR3, particularly when injected bilaterally into lagging muscle groups post-workout. The theory is that locally high concentrations activate satellite cells at the injection site. However, this has not been rigorously confirmed in controlled human studies, and systemic absorption still occurs regardless of injection site.
Does IGF-1 LR3 increase cancer risk?
Chronically elevated IGF-1 levels have been epidemiologically linked to increased risk of certain cancers, including colorectal, breast, and prostate cancer. IGF-1 promotes cell proliferation and inhibits apoptosis — mechanisms that can fuel tumor growth. While short-term, cycled use has not been directly linked to cancer in studies, anyone with a personal or family history of cancer should exercise extreme caution and consult with an oncologist before considering use.
How should IGF-1 LR3 be cycled?
The standard protocol is 4–6 weeks on followed by at least 4–6 weeks off. Continuous use is strongly discouraged due to receptor desensitization and the risk of organ enlargement and other serious side effects. During the off-cycle, the IGF-1 receptors resensitize, making subsequent cycles more effective. Some protocols alternate with MGF or MK-677 during off-periods.

References

  1. 1
    The insulin-like growth factor system: its role in the regulation of muscle mass and function(1996)PubMed ↗
  2. 2
    IGF-I stimulates muscle growth by suppressing protein breakdown and expression of atrophy-related ubiquitin ligases, atrogin-1 and MuRF1(2004)PubMed ↗
  3. 3
    Long R3 IGF-I is more potent than IGF-I in stimulating protein synthesis in L6 myoblasts(1996)PubMed ↗
  4. 4
    Circulating insulin-like growth factor I and cancer risk: a systematic review and meta-analysis(2020)PubMed ↗

Last updated: 2026-02-14