IGF-1 LR3
Also known as: Long R3 IGF-1
A laboratory reagent designed to keep cells growing in a dish, sold as a muscle builder on the strength of research that was never about muscle in people.
What it is
IGF-1 LR3 is a modified version of insulin-like growth factor 1, altered so it binds far less readily to the binding proteins that normally regulate it. That makes it much longer-lasting and more potent than the natural hormone. It was developed as a reagent for keeping cells growing in laboratory culture, and that is still what it is manufactured for.
Composition
A recombinant analogue of IGF-1 with an extended N-terminus and a single amino acid substitution. Sold online as a research chemical.
Proposed mechanism
IGF-1 mediates many of growth hormone's effects on tissue, binding its own receptor to promote cell growth, protein synthesis and survival. The modified analogue evades the binding proteins that would otherwise limit how much free hormone is available.
Claimed benefits
Muscle growth, including the claim — untested — that it produces new muscle cells rather than merely enlarging existing ones.
What the evidence shows
Unproven· in-vitro only. There are no human trials of this analogue for any of the claims made about it. The mechanism is real and the underlying hormone matters, but the specific proposition — that injecting this reagent builds muscle in people — has never been tested. The evidence base is cell culture and animal work, which is exactly what you would expect of a compound designed for cell culture.
Legal & regulatory status
Not a licensed medicine. IGF-1 and its analogues are prohibited at all times under the growth factors category of the WADA list.
Known risks & unknowns
Hypoglycaemia is the immediate danger: IGF-1 is structurally similar to insulin and can lower blood glucose, which at this analogue's potency is serious. There are also unresolved concerns about promoting the growth of existing tumours, since IGF-1 signalling drives proliferation and suppresses cell death generally rather than selectively in muscle. Long-term human safety data do not exist.
Sources
Frequently asked questions
- What is IGF-1 LR3?
- A modified version of insulin-like growth factor 1, altered so it binds far less readily to the binding proteins that normally regulate it — which makes it much longer-lasting and more potent. It was developed as a reagent to boost cell growth in laboratory culture, and that is what it is manufactured for.
- Does IGF-1 LR3 build muscle in humans?
- There are no human trials. IGF-1 genuinely mediates many of growth hormone's effects on tissue, and the mechanism sounds compelling, but the specific claim — that injecting this modified analogue produces muscle growth in people — has never been tested. The evidence base is cell culture and animal work.
- What are the risks?
- The one that matters most is hypoglycaemia: IGF-1 is structurally similar to insulin and can lower blood glucose, which at the potency of this analogue is a genuine danger. There are also unresolved concerns about promoting the growth of existing tumours, since IGF-1 signalling suppresses cell death and drives proliferation generally rather than selectively in muscle.
- Is it banned in sport?
- Yes. IGF-1 and its analogues are prohibited at all times under the growth factors category of the WADA list.
Related compounds
- MK-677 (Ibutamoren) (Silver)
An evidence-tiered explainer on MK-677 (ibutamoren): an oral ghrelin-receptor agonist, technically not a peptide, that raises GH and IGF-1, with real but modest human trial data and no approval.
- HGH Fragment 176-191 (Unproven)
An evidence-tiered explainer on HGH Fragment 176-191 / AOD-9604: a growth-hormone fragment marketed for fat loss whose largest human trial failed, leading its developer to abandon it.
- Follistatin-344 (Unproven)
An evidence-tiered explainer on Follistatin-344: the myostatin-blocking peptide sold on the back of a photograph of a very muscular mouse.
Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
Last reviewed: