IGF-1 LR3
Research highlights
- ✓An 83-amino-acid analogue of insulin-like growth factor 1
- ✓An N-terminal extension and arginine substitution give it a longer half-life
- ✓Most published work is in vitro or in rodent models
- ✓IGF-1 analogues appear on the WADA Prohibited List, banned at all times
What is IGF-1 LR3?
A recombinant analogue of insulin-like growth factor 1, 83 amino acids long: the native 70-residue sequence carrying an arginine in place of glutamic acid at position three, plus a 13-residue N-terminal extension. Those changes reduce its binding to IGF binding proteins, which is why it persists longer than native IGF-1.
What have researchers used it for?
Analogues of IGF-1 are common in laboratory work as supplements in serum-free cell-culture media, and in receptor-binding and cell-signalling assays. Researchers have also examined their behaviour in rodent models. The published evidence base is narrow, and very little of it involves humans.
IGF-1 LR3, explained
The short version: IGF-1 LR3 is an engineered version of insulin-like growth factor 1, with one amino acid swapped and an extra stretch of amino acids added to the front. Those changes stop most of the body's binding proteins from holding onto it, which made it several times more potent than normal IGF-1 in rats.
What it is
IGF-1 sits downstream of growth hormone: when growth hormone rises, IGF-1 follows, and it acts on tissues through its own receptor. IGF binding proteins latch onto IGF-1 in the body and blunt its activity.
LR3 stands for Long, Arginine 3. The glutamic acid at position 3 is replaced with arginine, and an extension is added at the start of the chain. Together those changes sharply cut its affinity for the binding proteins.
What has been studied
The key animal work comes from researchers in Adelaide, Australia, in the early 1990s. In a 1992 study in the Journal of Endocrinology, rats were made catabolic with the steroid dexamethasone and then given IGF-1 or analogues with weak binding-protein affinity, including LR3. Normal IGF-1 grew the gut, mainly by thickening its walls. LR3 did the same thing but was consistently several times more potent, which the authors took as evidence that binding proteins blunt the effect of injected IGF-1. They also concluded that the gut is one of the tissues most sensitive to IGF-1, and that potency in the body tracked how weakly each analogue bound those proteins.
Where the evidence stops
A 2026 review in Frontiers in Endocrinology found no peer-reviewed human studies of IGF-1 LR3 at all, and no documented human half-life. It placed the compound in its lowest evidence tier and flagged a theoretical concern about promoting cell growth, given what IGF-1 signalling does. WADA bans IGF-1 and its analogues at all times.
Handling and storage
It arrives as a freeze-dried powder. Once bacteriostatic water goes in, it belongs in the fridge. Our reconstitution and storage guide covers the details, and the calculator does the maths.
Built to dodge the binding proteins, and far stronger than IGF-1 in rat studies. In people it is a blank page.
Sources (checked 7 October 2026)
For research use only. Not for human consumption. Nothing on this page is medical advice.
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