IGF-1 LR3

IGF-1 LR3 is a synthetic analog of insulin-like growth factor 1, a naturally occurring protein hormone. It is modified to have a longer half-life than native IGF-1, allowing it to remain active in the body for extended periods. The peptide consists of 83 amino acids, with an additional arginine substitution at the third position and an extended amino acid chain compared to regular IGF-1.

IGF-1 LR3 is believed to promote muscle growth by stimulating protein synthesis and increasing cell proliferation. It may enhance fat metabolism and support recovery from exercise by improving tissue repair. Some studies suggest it can also aid in overall anabolic processes, contributing to strength and endurance improvements.

The main benefits of IGF‑1 LR3 appear to centre on muscle and tissue growth and regeneration. In animal research, infusion into late‑gestation fetal sheep led to increased weights of specific organs including heart and kidney and greater skeletal myoblast proliferation. More broadly, studies of the parent hormone IGF‑1 show it promotes muscle repair, increases muscle mass and supports cell survival via pathways such as PI3K/Akt ^{1, 2}.

Additional purported benefits include improved lean body composition and enhanced recovery from exercise‑induced damage. Some sources suggest higher IGF‑1 levels (and by extension analogues like IGF‑1 LR3) correlate with greater lean mass and reduced fat percentage in humans. The analog’s structural modifications result in lower binding to IGF‑binding proteins, increasing receptor availability and signalling potency ³. Overall, IGF‑1 LR3 enhances muscle and tissue growth, supports recovery, and improves lean body composition by increasing receptor signaling and promoting cell survival.

The synthetic analogue IGF‑1 LR3 has been shown in animal research to reduce insulin secretion in fetal sheep. In a study where fetal sheep received IGF‑1 LR3 infusions for one week, plasma insulin and glucose concentrations were lower compared to controls and glucose‑stimulated insulin secretion from isolated fetal islets was impaired. This suggests disruption of pancreatic β‑cell responsiveness may occur. Elevated levels of the parent hormone Insulin‑like growth factor 1 (IGF‑1) are also associated with increased cancer risk: women in the top 20 % of IGF‑1 concentration had a 1.24‑fold higher breast cancer risk compared to the bottom 20 % ^{4, 5}.

Additional negative effects linked to IGF‑1 analogues or elevated IGF‑1 levels include hypoglycaemia, tissue overgrowth and fluid retention. According to a review by the U.S. Anti‑Doping Agency, misuse of IGF‑1 compounds may lead to non‑reversible enlargement of the heart, joints and liver ⁶. In summary, IGF‑1 LR3 may impair insulin secretion, increase cancer risk and promote abnormal tissue growth and glucose regulation disturbances.

The analogue IGF‑1 LR3 binds to the IGF‑1 Receptor (IGF‑1R), a tyrosine‑kinase receptor on muscle, bone, fat and other tissues, causing the receptor to autophosphorylate and recruit adaptor proteins such as IRS‑1 and Shc. Studies in fetal sheep using an IGF‑1 analog showed activation of downstream signalling cascades in skeletal muscle after infusion. Once activated, signalling flows through two major pathways: the PI3K → Akt → mTOR pathway, which promotes protein synthesis and cell survival, and the Ras → Raf → MEK → ERK (MAPK) pathway, which stimulates cell proliferation and differentiation. The modification of IGF‑1 LR3 to reduce binding to IGF‑binding proteins (IGFBPs) increases its free concentration and receptor availability, thus enhancing and prolonging its signalling effect ⁷.

IGF‑1 LR3 is not approved by the Food and Drug Administration (FDA) for any therapeutic indication in humans. In sports, the World Anti‑Doping Agency (WADA) and its partners state all exogenous forms of IGF‑1 and its analogues are prohibited at all times under the Prohibited List. For example: “Insulin‐like Growth Factor 1 (IGF‑1) and its analogues … are prohibited substances in sport.” ⁸