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Growth Hormone — Extended IGF-1 Analog✓ FDA Approved

IGF-1 LR3

Also known as: Long Arginine IGF-1 · Insulin-like Growth Factor 1 LR3

MW

9111.4 Da

Amino Acids

83 AA

Half-Life

20-30 hours

Route

SubQ, IM

CAS

946870-92-4

Mechanism of Action

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified IGF-1 with an arginine substitution at position 3 and a 13-amino acid N-terminal extension. These modifications reduce IGFBP (IGF binding protein) binding by >95%, resulting in dramatically higher free IGF-1 bioavailability and extended half-life (20–30 hours vs 12–15 minutes for native IGF-1).

PRIMARY MECHANISM — IGF-1R ACTIVATION: Binds IGF-1 receptor → autophosphorylation → PI3K/AKT/mTOR pathway activation → potent protein synthesis, satellite cell proliferation, nitrogen retention. This is the most direct anabolic signaling pathway — bypassing the GH step entirely.

SATELLITE CELL ACTIVATION: Directly stimulates muscle satellite cell proliferation and differentiation → myoblast fusion → new myofiber formation. This is genuine muscle hyperplasia (new fibers), not just hypertrophy (bigger existing fibers).

ANTI-CATABOLIC: Suppresses muscle protein breakdown via AKT-mediated FOXO phosphorylation (inactivation of atrophy genes).

HYPOGLYCEMIA RISK: IGF-1 shares ~60% structural homology with insulin and binds the insulin receptor at high concentrations. At therapeutic doses, IGF-1 LR3 produces insulin-like glucose-lowering effects — hypoglycemia is a real and dangerous risk.

Dosing Protocol

Low Dose

███ – ███ mcg/day

Standard Dose

███ mcg/day

High Dose

███ – ███ mcg/day

Dosing protocols are for paid members

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Frequency

Daily.

Half-Life

20-30 hours

Reconstitution Guide

Full reconstitution protocol with BAC water volumes, concentration math, and units-to-draw per dose is available on the Clinical plan.

Unlock reconstitution guide →

Clinical Warnings

HYPOGLYCEMIA RISK — always have fast-acting glucose available.

Cancer risk from sustained IGF-1R activation (mitogenic).

Organ growth (intestinal, cardiac hypertrophy).

Suppresses endogenous GH/IGF-1 axis.

WADA prohibited.

NOT same as clinical IGF-1 (mecasermin/Increlex).

Dose carefully — narrow therapeutic window.

Contraindications

Absolute

Active cancer

Pregnancy

Diabetic retinopathy

Relative Cautions

Diabetes

History of cancer

Organ hypertrophy concerns

Side Effect Profile

Mild

  • Injection site pain
  • Mild hypoglycemia
  • Headache

Moderate

  • Hypoglycemia
  • Joint pain
  • Jaw/hand growth

Severe (Rare)

  • Organ growth
  • Cancer proliferation
  • Severe hypoglycemia

Synergistic Peptides

CJC-1295MK-677GHRP-2

Common Stacks

CJC-1295

MK-677

Research Status

Well-characterized pharmacology. PMID 7629959 (Tomas 1994): Extended half-life and reduced IGFBP binding. PMID 8568916 (Clark 1996): Muscle anabolic effects. No approved human therapeutic use for LR3 form. Clinical IGF-1 (mecasermin/Increlex) is native form.

Frequently Asked Questions

How does IGF-1 LR3 work?

IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified IGF-1 with an arginine substitution at position 3 and a 13-amino acid N-terminal extension. These modifications reduce IGFBP (IGF binding protein) binding by >95%, resulting in dramatically higher free IGF-1 bioavailability and extended half-life (20–30 hours vs 12–15 minutes for native IGF-1). PRIMARY MECHANISM — IGF-1R ACTIVATION: Binds IGF-1 receptor → autophosphorylation → PI3K/AKT/mTOR pathway activation → potent protein synthe

What is the standard dose of IGF-1 LR3?

IGF-1 LR3 dosing protocols are available with a ClinPep Clinical subscription. Dosing varies by indication and patient factors — consult a licensed healthcare provider. General frequency: Daily.

What is the half-life of IGF-1 LR3?

The half-life of IGF-1 LR3 is 20-30 hours. This determines optimal dosing frequency and timing.

Who should not use IGF-1 LR3?

IGF-1 LR3 is absolutely contraindicated in: Active cancer; Pregnancy; Diabetic retinopathy. Use with caution in: Diabetes; History of cancer; Organ hypertrophy concerns.

What are the side effects of IGF-1 LR3?

Common mild side effects include: Injection site pain, Mild hypoglycemia, Headache. Moderate effects: Hypoglycemia, Joint pain, Jaw/hand growth.

What peptides stack well with IGF-1 LR3?

IGF-1 LR3 is commonly stacked with: CJC-1295, MK-677, GHRP-2.

How do you reconstitute IGF-1 LR3?

IGF-1 LR3 is reconstituted with bacteriostatic water. Exact volumes, concentrations, and units-to-draw calculations are available in the ClinPep Clinical plan. Always follow your compounding pharmacy's instructions.

How long should you cycle IGF-1 LR3?

IGF-1 LR3 cycle protocols vary by indication. Detailed cycle length, on/off schedules, and monitoring guidelines are available with ClinPep Clinical access. Consult your healthcare provider for personalized cycling guidance.

References & Citations

10 PubMed studies · 3 clinical trials

Provisional Treatment of Volumetric Muscle Loss With Insulin-like Growth Factor 1 Releasing Muscle Void Fillers.

Clark Andrew R, Adams Alex T, McKinley Todd O, Natoli Roman M et al.. The Journal of surgical research. 2026

PubMed: 41418663DOI ↗C — Research Article

Volumetric muscle loss (VML) resulting from severe extremity injuries in combat remains a significant clinical challenge, particularly in austere environments. Current research emphasizes the developm

Revolutionary decellularized Alstroemeria stem-based nerve conduit integrated with GelMA and controlled IGF-1 LR3 release for enhanced rat sciatic nerve regeneration.

Yavuz Ersin, Sağır Melih S, Ercan Alp, Erginer Merve et al.. International journal of biological macromolecules. 2025

PubMed: 41015370DOI ↗C — Research Article

Peripheral nerve injuries lead to significant functional deficits, with no treatment achieving complete recovery. Autologous nerve grafting remains the gold standard, but it is limited by donor site m

IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep.

White Alicia, Stremming Jane, Wesolowski Stephanie R, Al-Juboori Saif I et al.. American journal of physiology. Endocrinology and metabolism. 2025

PubMed: 39679943DOI ↗C — Research Article

Insulin-like growth factor-1 (IGF-1) and insulin are important fetal anabolic hormones. Complications of pregnancy, such as placental insufficiency, can lead to fetal growth restriction (FGR) with low

Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice.

Engel Matthew G, Narayan Sushma, Cui Min-Hui, Branch Craig A et al.. Journal of Alzheimer's disease : JAD. 2025

PubMed: 39610283DOI ↗C — Research Article

Insulin-like growth factor-1 (IGF-1) promotes neurogenesis, cell survival, and glial function, making it a promising candidate therapy in Alzheimer's disease (AD). Long arginine 3-IGF-1 (LR3-IGF-1) is

Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris.

Lu Zequn, Liu Ning, Huang Huoqing, Wang Yuan et al.. Applied microbiology and biotechnology. 2023

PubMed: 37261455DOI ↗C — Research Article

Insulin-like growth factor-1 (IGF-1) is a pleiotropic protein hormone and has become an attractive therapeutic target because of its multiple roles in various physiological processes, including growth

Attenuated glucose-stimulated insulin secretion during an acute IGF-1 LR3 infusion into fetal sheep does not persist in isolated islets.

White Alicia, Stremming Jane, Brown Laura D, Rozance Paul J. Journal of developmental origins of health and disease. 2023

PubMed: 37114757DOI ↗C — Research Article

Insulin-like growth factor-1 (IGF-1) is a critical fetal growth hormone that has been proposed as a therapy for intrauterine growth restriction. We previously demonstrated that a 1-week IGF-1 LR3 infu

N-Linked Glycosylation in Chinese Hamster Ovary Cells Is Critical for Insulin-like Growth Factor 1 Signaling.

Salvi Rupashree, Kumar Chandan, Brahmbhatt Krupanshi, Subedi Rambhadur et al.. International journal of molecular sciences. 2022

PubMed: 36499281DOI ↗C — Research Article

Cell surface proteins carrying N-glycans play important roles in inter- and intracellular processes including cell adhesion, development, and cellular recognition. Dysregulation of the glycosylation m

Reduced glucose-stimulated insulin secretion following a 1-wk IGF-1 infusion in late gestation fetal sheep is due to an intrinsic islet defect.

White Alicia, Stremming Jane, Boehmer Brit H, Chang Eileen I et al.. American journal of physiology. Endocrinology and metabolism. 2021

PubMed: 33938236DOI ↗C — Research Article

Insulin and insulin-like growth factor-1 (IGF-1) are fetal hormones critical to establishing normal fetal growth. Experimentally elevated IGF-1 concentrations during late gestation increase fetal weig

Registered Clinical Trials

QUILT-2.017: Phase 1b/2 Study of AMG 479 in Combination With Paclitaxel and Carboplatin for 1st Line Treatment of Advanced Squamous Non-Small Cell Lung Cancer

NCT00807612TERMINATEDPHASE1, PHASE2

Adapted Physical Activity (APA) in a Breast Cancer Population.

Effectiveness of NMES Associated to Vascular Occlusion in Functional Performance and Muscle Hypertrophy in Athlete's

NCT02406339COMPLETEDNA

Symptom Indications

Muscle growthRecoveryAnti-catabolicHyperplasia

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This information is for educational and research reference purposes only. ClinPep does not provide medical advice, diagnosis, or treatment recommendations. All protocols should be reviewed by a licensed healthcare provider.