COMPOUND

Compounds / GH secretagogues

IGF-1 LR3

Long Arg-3 Insulin-like Growth Factor-1 (LongR3 IGF-1)

GH secretagogues SubQ · IM Not FDA approved

Modified analog of human IGF-1 with an N-terminal 13aa extension and arginine-3 substitution. Binds IGF-1 receptor with full agonism but binds IGFBPs ~100x weaker, so circulates 'free' and unprotected, extending half-life from ~10-15 minutes (native IGF-1) to ~20-30 hours. Used in bodybuilding for muscle hypertrophy. CRITICAL WARNINGS: (1) HYPOGLYCEMIA RISK: insulin-mimetic action can cause severe hypoglycemia within 30-60 min of injection; always carry a fast-acting glucose source and eat carbs within 30 min of dose. (2) CANCER RISK: IGF-1 is a known mitogen and inhibits apoptosis; sustained elevated IGF-1 is epidemiologically associated with prostate, breast, and colorectal cancer risk. AVOID in any personal or family history of cancer.

At a glance

Half-life
~24 h Reported range 20-30 hours due to reduced IGFBP binding (vs ~10-15 min for native IGF-1). Some older sources cite ~12.5h (likely reflects specific assay conditions); modern community consensus is 20-30h. Tmax ~30 min.
Routes
SubQ · IM
Vial sizes
1 mg
Evidence base
3 studies 1 human · 1 review · 1 preclinical

Mechanism

Binds IGF-1 receptor on muscle, bone, and many other tissues. Activates PI3K/Akt/mTOR pathway → protein synthesis, satellite cell proliferation, anti-apoptosis. Drives glucose uptake via GLUT4 (insulin-mimetic action). Stimulates differentiation of muscle precursors to mature myocytes. Reduced IGFBP binding means more 'free' IGF-1 receptor signaling per unit dose vs native IGF-1, and a much longer effective tissue exposure. LR3 was several-fold more anabolic than native IGF-1 in dexamethasone-induced wasting model. Native IGF-1 IGFBP-binding/clearance established as the PK baseline. High circulating IGF-1 associated with increased prostate and premenopausal breast cancer risk.

Dosing

Any amounts shown here are reported from published studies only. 1 of 3 catalogued studies involved human subjects. COMPOUND does not publish its own dosing guidance.

Published evidence

  1. Meta-analysis 2004

    IGF-I, IGFBP-3, and cancer risk: systematic review and meta-regression analysis

    Renehan AG, Zwahlen M, Minder C, et al. Lancet

    Meta-analysis: high circulating IGF-1 associated with increased risk of prostate and premenopausal breast cancer. Foundational citation for cancer concern with exogenous IGF-1 use.

    PMID 14726171

  2. Human observational 1993

    Pharmacokinetics of recombinant human insulin-like growth factor-I in growth hormone insensitive children

    Heinrichs C, Vis HL, Bergmann P, et al. Eur J Endocrinol

    Established native IGF-1 PK: short t½ due to IGFBP binding/clearance. Foundational for understanding why LR3 modification dramatically extends exposure.

    PMID 8219484

  3. Animal in vivo 1992

    Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats

    Tomas FM, Knowles SE, Owens PC, et al. Biochemical Journal

    Foundational animal data: IGF-1 LR3 was several-fold more anabolic than native IGF-1 in dexamethasone-induced wasting model.

    PMID 1371669

Reported side effects

Hypoglycemia
Common Serious · Most acute risk: can cause severe hypoglycemia within 30-60 min if injected fasted or with inadequate carbohydrate intake. Higher doses combined with skipped meals have resulted in emergency department presentations.
Hypoglycemia symptoms
Common Moderate · Sweating, shakiness, dizziness, hunger, brain fog, confusion.
Mitogenic / cancer risk (theoretical)
Unknown Serious · Sustained elevated IGF-1 epidemiologically associated with prostate, breast, colorectal cancer risk (Renehan 2004 Lancet meta-analysis). No RCT evidence of causation in supraphysiologic exogenous use, but mechanistically plausible: IGF-1 is a known mitogen and inhibits apoptosis. Pre-existing tumors theoretically accelerated. AVOID with any cancer history.
Organ overgrowth (acromegaly-like)
Occasional Moderate · Hands, feet, jaw growth with chronic supraphysiologic doses. Reversible if discontinued early.
Insulin resistance
Occasional Moderate · Long-term high-dose use can downregulate insulin signaling.
Gut / intestinal growth
Occasional Mild · IGF-1 is trophic to gut epithelium. Some users report increased waist/intestinal mass ('GH/IGF gut'). Cosmetic concern.
Injection site reaction
Common Mild · Local redness, mild pain.

Interactions

  • Insulin Contraindicated

    Both lower blood glucose. Combined hypoglycemia risk is severe. Bodybuilders sometimes stack but ER risk is real and documented.

  • CJC-1295 (no DAC) Caution

    GH-driven endogenous IGF-1 + exogenous IGF-1 LR3 creates supraphysiologic IGF-1 exposure. Common stack but compounds mitogenic risk.

  • CJC-1295 (DAC) Caution

    Sustained GH elevation (DAC) + exogenous IGF-1 LR3 amplifies supraphysiologic IGF-1 exposure more than No-DAC variant. Mitogenic risk + insulin resistance.

  • Test Cypionate Synergy

    Anabolic synergy on muscle protein synthesis. Standard bodybuilding stack.

Reconstitution and storage

1mg vial + 1mL BAC water → 1000 mcg/mL. 0.04mL = 40 mcg.

Lyophilized at -20°C. Reconstituted refrigerated, use within 14 days (more degradation-prone than other peptides).

Open the reconstitution calculator for IGF-1 LR3