What it is
IGF-1 LR3 (Long R3 insulin-like growth factor-1) is an extended-half-life analog of IGF-1, a growth factor involved in tissue growth. It is studied preclinically for muscle hyperplasia (an increase in the number of muscle cells), protein synthesis and recovery.
IGF-1 biology itself is extensively studied, but the LR3 analog is a research reagent rather than a clinical drug. In the PeptidesAI encyclopedia it is categorized under growth hormone.
How it's thought to work
It binds IGF-1 receptors to drive protein synthesis, cell proliferation and satellite-cell activation, where satellite cells are the stem cells of muscle tissue. The LR3 modification reduces its binding to IGF-binding proteins, the blood proteins that bind and carry IGF-1, and is described as greatly extending its half-life and activity.
In a rat study, IGF-1 variants that bind poorly to IGF-binding proteins, including LR3, were about 2.5-fold more potent than IGF-1 at reversing the body weight loss and nitrogen loss produced by a corticosteroid.
What the research says
IGF-1 biology is extensively studied; the LR3 analog itself is a research reagent, not a clinical drug. The published work on LR3 cited here is in animals.
In pigs, IGF-1 variants with reduced affinity for IGF-binding proteins, including LR3, lowered blood glucose 2- to 3-fold more strongly than IGF-1, and over a longer period.
Reported side effects
Reported side effects include hypoglycemia (low blood sugar), headache and injection site reactions. A theoretical concern is that strong growth signaling could promote unwanted tissue growth. The animal glucose-lowering findings above are consistent with the hypoglycemia concern.
Reconstitution
IGF-1 LR3 is supplied as a lyophilized (freeze-dried) powder and is typically reconstituted with bacteriostatic (BAC) water before use. It commonly comes in 1 mg vials. The amount of peptide in the vial is fixed; the water added only changes how concentrated the solution is.
Worked example. A 1 mg vial is 1,000 mcg. Reconstituted with 1 mL of BAC water, that works out to 1,000 mcg ÷ 1 mL = 1,000 mcg/mL. On a U-100 insulin syringe, where each unit is 0.01 mL, each unit holds 1,000 × 0.01 = 10 mcg. Use the peptide reconstitution calculator to work out the concentration and units for any vial size and water volume.
Important notes
IGF-1 LR3 is a growth factor with significant safety considerations, including hypoglycemia and a theoretical risk of tissue growth. It is not FDA-approved and is listed as prohibited by the World Anti-Doping Agency (WADA).
Sources
- Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Tomas FM et al. Biochemical Journal, 1992. Preclinical
- IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. Tomas FM et al. Journal of Endocrinology, 1997. Preclinical
Frequently asked questions
These questions cover the same ground as the sections above, in a shorter format.
What is IGF-1 LR3?
An extended-half-life analog of IGF-1, studied preclinically for muscle hyperplasia, protein synthesis and recovery.
How is IGF-1 LR3 thought to work?
It binds IGF-1 receptors to drive protein synthesis, cell proliferation and satellite-cell activation, and its reduced binding to IGF-binding proteins is described as extending its half-life and activity.
What does the research on IGF-1 LR3 say?
IGF-1 biology is extensively studied, but LR3 itself is a research reagent; the published work cited here is in animals, where LR3 and similar variants were more potent than IGF-1.
What are the reported side effects of IGF-1 LR3?
Hypoglycemia, headache and injection site reactions, plus a theoretical concern about unwanted tissue growth.
How much is one unit from a 1 mg IGF-1 LR3 vial?
With 1 mL of BAC water, a 1 mg vial is 1,000 mcg/mL, so one unit on a U-100 syringe (0.01 mL) holds 10 mcg.
The full entry, plus the calculator
The PeptidesAI app has the complete encyclopedia entry for IGF-1 LR3 — one of 70 compounds covered — plus the reconstitution calculator, a dose log and reminders. Free to download on iPhone.
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