IGF-1 LR3

IGF-1 LR3 (Long R3 IGF-1) is an engineered version of insulin-like growth factor 1 that acts on the IGF-1 receptor. Researchers built it in the early 1990s as a lab reagent for studying how IGF-1 works, not as a medicine. Its two changes, an arginine at position 3 and a 13-amino-acid extension at the start, make it bind very weakly to IGF-binding proteins, which is why it was more potent than natural IGF-1 in cell and rat studies. No peer-reviewed study has tested it in people.

No. Mecasermin (Increlex) is recombinant human IGF-1: 70 amino acids with the same sequence as the IGF-1 your body makes. The FDA approved it for growth failure in children 2 years and older with severe primary IGF-1 deficiency, or a growth hormone gene deletion with antibodies that block growth hormone. Its label says it is not a substitute for growth hormone. It comes as a ready-made 40 mg/4 mL (10 mg/mL) solution, kept in the fridge and used within 30 days of first opening. IGF-1 LR3 is a different molecule, no approved product contains it, and none of the Increlex label’s data describe it.

It is a real concern, but it has not been measured in people. IGF-1 has insulin-like effects: the Increlex label reports severe low blood sugar leading to seizures, and 42% of children in its trials had low blood sugar at least once. Because of that, the label ties every Increlex injection to a meal or snack and warns against driving or exercise in the hours after a dose, especially early in treatment. A 2026 review says reports of IGF-1 LR3 side effects center on symptoms that suggest low blood sugar, but most come from non-clinical sources.

Nobody knows, because there are no long-term human data. A 2026 review calls the risk theoretical but clinically relevant: population studies link higher IGF-1 levels with several cancers, including breast and prostate cancer, though that does not show any peptide causes cancer. The approved IGF-1 medicine, Increlex, must not be used in children with cancer or a history of it, and its label says to monitor every patient for new tumors.

Yes. The 2026 WADA Prohibited List bans “Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues” at all times, in and out of competition. IGF-1 LR3 is not named, but it is an IGF-1 analogue, and the list also covers substances with a similar chemical structure or biological effect. In 2010, an anti-doping lab reported finding a His-tagged form of it in a black-market vial.

There is no single correct amount. The water only sets the concentration: mg in the vial ÷ mL of water = mg per mL. For example (numbers for illustration only, not a dose), 1 mg of IGF-1 LR3 in 1 mL makes 1 mg/mL, so each unit on a U-100 insulin syringe holds 0.01 mg (10 mcg). The same vial in 2 mL makes 0.5 mg/mL, or 0.005 mg (5 mcg) per unit. More water means each unit holds less; less water means each unit holds more. The reconstitution calculator does this arithmetic for your vial. Increlex, the approved IGF-1, needs no mixing: it comes as a ready-made solution. Because this product is not FDA-approved, no official label sets a water volume, and the contents of unapproved vials are not verified. Talk to a licensed prescriber or pharmacist before using any unapproved product. Our guide to how to reconstitute peptides covers the steps.