Also known as: Long R3 IGF-1 · Insulin-like Growth Factor-1 LR3
IGF-1 LR3 is a synthetic analog of Insulin-like Growth Factor 1 (IGF-1) with a 13-amino-acid N-terminal extension and a glutamic acid to arginine substitution at position 3. These modifications reduce IGFBP binding by ~500-fold, resulting in a half-life of 20–30 hours versus ~15 minutes for native IGF-1, with full retention of anabolic potency.
IGF-1 LR3 was developed to overcome the major pharmacological limitation of native IGF-1: its rapid sequestration by Insulin-like Growth Factor Binding Proteins (IGFBPs), particularly IGFBP-3, which complex with >99% of circulating IGF-1 and dramatically limit its bioavailability. The LR3 modification (Long-chain extension at position R3) sterically hinders IGFBP binding while preserving full IGF-1 receptor affinity.
In skeletal muscle, IGF-1 LR3 drives both hypertrophy (enlarged muscle fiber size) and hyperplasia (increased muscle cell number by activating satellite cells) — a distinction from androgens, which primarily drive hypertrophy alone. This dual mechanism makes IGF-1 LR3 a compound of significant research interest in muscle wasting diseases, cachexia, and sports medicine.
IGF-1 LR3 binds the IGF-1 receptor with affinity equivalent to native IGF-1, activating the receptor's intrinsic tyrosine kinase. Downstream signaling through PI3K/Akt/mTOR drives protein synthesis and inhibits muscle protein breakdown (anti-catabolism) through FoxO phosphorylation.
IGF-1 LR3 activates muscle satellite cells (myogenic stem cells) — promoting their proliferation and fusion into existing muscle fibers. This generates true hyperplasia (new myonuclei) which may explain permanent muscle adaptation even after cessation of use.
Like native IGF-1, LR3 activates insulin receptors with ~10% the potency of insulin. At high doses this can cause hypoglycemia — a key safety consideration. Carbohydrate co-administration is standard practice in research protocols.
IGF-1 LR3 is a potent anabolic agent — its extended half-life means systemic IGF-1R stimulation for 20–30 hours per dose. Hypoglycaemia is the primary safety concern: IGF-1 shares structural homology with insulin and stimulates glucose uptake. Never administer fasted without glucose available. Always eat within 15–20 min of injection. Monitor blood glucose if possible. Due to IGF-1's role in cellular proliferation, IGF-1 LR3 is not appropriate for individuals with pre-existing cancer, elevated cancer risk, or active growth-plate age (under ~21). Source from reputable suppliers with verified purity.
IGF-1 LR3 cycles are intentionally short due to receptor desensitisation (IGF-1R downregulation with prolonged stimulation) and to minimise cumulative cellular proliferation stimulus. 4-week cycles are standard; 6 weeks is the practical maximum in research protocols. The off-cycle should be at least equal in duration to the on-cycle. Unlike GH secretagogues that preserve pulsatile regulation, IGF-1 LR3 provides continuous receptor stimulation that requires strict cycling.
IGF-1 LR3 is one of the most potent peptides in this category. Hypoglycaemia risk is real and dose-dependent. Potential mitogenic effects (stimulation of cell growth including abnormal cells) are a theoretical concern with any IGF-1 pathway activator. Cycle length and dosing should be conservative. Not for use alongside other strong anabolic agents without understanding cumulative risks.
Ask anything about IGF-1 LR3 — mechanisms, dosing protocols, interactions, or research comparisons.
BPC-157 is a synthetic pentadecapeptide (15 amino acids) isolated from human gastric juice protein BPC. It demonstrates…
TB-500 is a synthetic version of Thymosin Beta-4 (Tβ4), a naturally occurring 43-amino-acid peptide found in virtually a…
CJC-1295 without DAC (Modified GRF 1-29) is a GHRH analogue with four stabilising amino acid substitutions that extend i…
Ipamorelin is a selective pentapeptide growth hormone releasing peptide (GHRP) that stimulates pituitary GH release with…