Recovery & Repair · Compounded 503A · Subcutaneous
IGF-1 LR3: the long-acting growth factor for tissue repair.
IGF-1 LR3 (Long Arg3 IGF-1) is a synthetic 83-amino-acid analog of insulin-like growth factor 1, modified to resist binding by IGFBPs (IGF binding proteins) and to extend half-life. The result is a more bioavailable, longer-acting form of IGF-1 — used clinically for muscle protein synthesis and tissue repair.
What IGF-1 LR3 is
IGF-1 LR3 is a synthetic 83-amino-acid analog of native IGF-1, with two modifications: substitution of arginine for glutamic acid at position 3 (the 'R3') and an extension of 13 amino acids at the N-terminus (the 'L' for long). The combined effect is dramatically reduced binding to IGF binding proteins and a half-life roughly 20× that of native IGF-1.
Native IGF-1 circulates almost entirely bound to IGFBPs — predominantly IGFBP-3 — which both extend its half-life and limit its tissue bioavailability. IGF-1 LR3 escapes this sequestration. Free IGF-1 reaches the IGF-1 receptor on target tissues more readily.
IGF-1 LR3 is not FDA-approved. Compounded IGF-1 LR3 is dispensed by licensed 503A pharmacies under physician prescription for off-label use — typically for muscle protein synthesis, recovery from injury, and tissue repair.
How it works
IGF-1 LR3 binds the IGF-1 receptor on muscle, tendon, ligament, and other target tissues. Receptor activation triggers the PI3K-Akt-mTOR pathway, which drives ribosomal biogenesis, muscle protein synthesis, and satellite-cell activation.
By bypassing IGFBP sequestration, IGF-1 LR3 produces a larger and longer free-IGF-1 signal than native IGF-1 at equivalent doses. This is why much smaller doses (typically 20–50 mcg) produce meaningful effect.
Downstream, IGF-1 LR3 supports muscle hypertrophy, satellite cell proliferation, connective tissue repair, and (in some preclinical models) neuroprotective effects. Clinical use focuses primarily on the muscle and tissue-repair effects.
What patients use it for
Muscle protein synthesis
Direct activation of the IGF-1 receptor on skeletal muscle. The strongest mechanistic case — IGF-1 LR3 drives protein synthesis even in the absence of resistance training, with much larger effect when paired with it.
Satellite cell activation
Satellite cells are the muscle's resident stem cells. Their activation is required for muscle repair after exercise and injury. IGF-1 LR3 supports this activation.
Tissue and tendon repair
IGF-1 activity is required for normal tendon and ligament healing. IGF-1 LR3 is often used as a tissue-repair adjunct, sometimes alongside BPC-157 and TB-500.
Extended half-life
Roughly 20× the half-life of native IGF-1. Enables once-daily or even less frequent dosing instead of multiple doses per day.
Evidence summary
IGF-1 LR3 was originally developed as a research tool for cell-culture studies of IGF-1 signaling and is widely used in that context. Translational human evidence specific to IGF-1 LR3 (as distinct from rhIGF-1, mecasermin) is limited.
Mecasermin (rhIGF-1, brand Increlex) is FDA-approved for severe primary IGF-1 deficiency in children and provides the closest human safety/efficacy reference for IGF-1 receptor agonism.
Off-label IGF-1 LR3 use for muscle and recovery is supported by strong cell-biology evidence and clinical experience but is not backed by large human RCTs. This is honest framing — the mechanism is well-characterized; the human outcome RCTs at typical compounded doses are not.
Dosing and clinical context
General clinical context only. Kindr Health physicians determine the appropriate dose and protocol for each patient based on history and labs. This is not a prescription or dosing recommendation.
Typical clinical protocols use 20–50 mcg subcutaneously, once daily. Some protocols use post-workout subcutaneous injection near the trained muscle group.
Course length is typically 4–6 weeks with reassessment, often followed by a break of similar length. Continuous long-term use is not the standard pattern.
Often used alongside resistance training or as part of post-injury rehab. Pure pharmacologic use without exercise is not the typical protocol.
Safety and contraindications
Common side effects: hypoglycemia (IGF-1 has insulin-like effects on glucose uptake), injection-site reaction, transient joint pain, mild headache.
Contraindications: pregnancy, active malignancy (IGF-1 promotes proliferation), severe untreated diabetes, active retinopathy. Patients with cancer history require careful evaluation.
Baseline labs required: IGF-1, fasting glucose, lipid panel. Monitoring during therapy is the norm. Off-label compounded use under physician supervision through a licensed 503A pharmacy.
Who it's typically considered for
- Adults with documented age-related lean-mass loss and a structured training program
- Athletes in post-injury rehab where additional muscle and tissue support is appropriate
- Patients on or considering GH-axis support (sermorelin, CJC-1295, ipamorelin) who have a specific muscle or repair goal
- Patients with no active malignancy and no significant cancer history
Frequently asked questions
Is IGF-1 LR3 the same as HGH?
No. HGH (growth hormone) is the upstream signal. IGF-1 is one of the downstream effectors that HGH produces — and IGF-1 LR3 is a modified form of IGF-1 with longer half-life and reduced binding-protein sequestration. The two are different molecules with related but distinct effects.
Is IGF-1 LR3 FDA-approved?
No. Mecasermin (rhIGF-1, Increlex) is FDA-approved for severe primary IGF-1 deficiency in children, but IGF-1 LR3 itself is not. Compounded IGF-1 LR3 is prepared by 503A pharmacies for off-label use under physician prescription.
Is IGF-1 LR3 banned in sports?
Yes. The World Anti-Doping Agency (WADA) prohibits IGF-1 and its analogs in athletic competition. Competitive athletes subject to drug testing should not use IGF-1 LR3 without consulting their governing body.
Can IGF-1 LR3 cause low blood sugar?
Yes — it can. IGF-1 has insulin-like activity on glucose uptake. Hypoglycemia is the most predictable side effect, particularly at higher doses or when food intake is irregular. Most protocols dose around meals to mitigate this.
Is IGF-1 LR3 safe in cancer survivors?
IGF-1 signaling supports cell proliferation, which is mechanistically concerning in active cancer. In cancer survivors with no active disease, use should be discussed with both the prescribing physician and the patient's oncologist before initiating.
Why is it called "LR3"?
The L stands for the 13-amino-acid N-terminal extension that extends half-life. The R3 refers to the arginine substitution at position 3 — replacing glutamic acid. Together these modifications reduce binding-protein sequestration and extend pharmacological activity.
Does IGF-1 LR3 work without exercise?
Partially. The pharmacology drives protein synthesis directly. But the published evidence and clinical experience are consistent that the muscle response is substantially larger when IGF-1 LR3 is paired with resistance training. Pharmacology + training is the standard pattern.
Sources
- Tomas FM et al. Insulin-like growth factor (IGF)-I but less potently IGF-II is preferentially incorporated into adipose tissue lipid in growing rats. Journal of Endocrinology (1993). — pubmed.ncbi.nlm.nih.gov/8409997
- Frystyk J. The growth hormone hypothesis — 2005 revisited. Hormone and Metabolic Research (2003). — pubmed.ncbi.nlm.nih.gov/14668941
- FDA — Increlex (mecasermin) prescribing information. — www.accessdata.fda.gov/drugsatfda_docs/label/2007/021839s003lbl.pdf
- Adams GR. Invited Review: Autocrine/paracrine IGF-I and skeletal muscle adaptation. Journal of Applied Physiology (2002). — pubmed.ncbi.nlm.nih.gov/12235048
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Medically reviewed by Dr. Ana Lisa Carr, MD, MBA
Board-Certified Family Medicine Physician · Lead Provider / Medical Reviewer
NPI 1689841744 · Last reviewed: May 10, 2026
Last reviewed May 10, 2026. Compounded medications are prepared by FDA-registered 503A pharmacies and are not FDA-approved drug products. Prescriptions require a clinical evaluation; a Kindr Health physician determines eligibility. Not for use in pregnancy. This page provides educational information and is not medical advice.