IGF-1 LR3
Long Arginine 3 Insulin-like Growth Factor 1
Long-acting IGF-1 analog for anabolic signaling
About
IGF-1 LR3 is a synthetic 83-amino-acid analog of human IGF-1 with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. These modifications reduce binding to IGF-binding proteins, extending its half-life roughly 2-3x versus native IGF-1. It is widely used in research contexts for muscle protein synthesis studies and has no published human clinical trials of its own.
Mechanism
Binds IGF-1R with high affinity and activates PI3K/Akt/mTOR (protein synthesis, glucose uptake) and RAS/RAF/MEK/ERK (proliferation) pathways.
Dosage
Draw to 8 units on a U-100 insulin syringe
1 mg · 2 mL BAC
When to take: Post-workout on training days; morning with food on rest days. Never inject fasted and never within 2 hours of bedtime. Consume 30-50g fast-acting carbohydrate within 30 minutes of injection.
Reconstitution
Vial size (mg): 1 mg · BAC water (mL): 2 mL · Concentration: 500 mcg/mL
50 mcg dose = 10 units on a U-100 insulin syringe.
Benefits
- Enhanced muscle protein synthesis
- Anti-catabolic support during training
- Possible localized hypertrophy with site-specific IM injection
- Improved nutrient partitioning and glucose uptake into muscle
Side effects
- Hypoglycemia (reported in ~42% of Increlex subjects, can be severe)
- Lymphoid/tonsillar hypertrophy
- Visceral organ growth (kidney, spleen) — largely irreversible
- Fluid retention, joint discomfort, headaches
- Injection-site lipohypertrophy
- Possible feedback suppression of endogenous GH
Gender notes
Cautions
- Active or prior cancer history (mitogenic concern)
- Diabetes or glucose dysregulation
- Concurrent insulin or sulfonylurea therapy
- Pregnancy and breastfeeding
- Pre-existing cardiac, kidney, liver, or splenic disease
- Adolescents with open growth plates
Research
- Anabolic effects of insulin-like growth factor-I (IGF-I) variants in normal female rats
Journal of Endocrinology · 1996
Tomas et al. demonstrated that IGF-1 analogs with reduced IGFBP binding (including LR3) maintain superior anabolic potency versus native IGF-1 when injected, supporting protein retention in rat models.
- Mecasermin (recombinant human IGF-1) for the treatment of short stature
Expert Opinion on Biological Therapy · 2007
Pivotal Increlex data document hypoglycemia in ~42% of pediatric subjects and tonsillar hypertrophy in ~15%, informing the safety expectations for IGF-1 analog use.
- Detection of IGF-1 LR3 in human urine by mass spectrometry
Drug Testing and Analysis · 2020
First validated WADA detection assay for IGF-1 LR3, confirming its abuse in sport and its banned status under category S2.