What it is
IGF-1 LR3, or Long R3 IGF-I, is a modified analog of human insulin-like growth factor 1. Arginine replaces glutamate at position 3 and a 13-residue extension is added at the N-terminus, changes that sharply lower its affinity for IGF binding proteins. It is used chiefly as a research reagent in cell culture, livestock physiology and animal models.
How it works
It signals through the type 1 IGF receptor in the same way as native IGF-1. Because it binds IGF binding proteins weakly, a larger fraction is thought to stay free and receptor-available. That is the basis for its use as a potent analog in laboratory work.
Regulatory status
- Cosmetic ingredient
- Research compound
- In clinical trials
- Approved medicine
Not approved as a medicine by the FDA or the EMA. Some are registered in individual countries. Supplied for laboratory research only.
What published research is studying
- Organ and tissue growth responses to IGF analogs in animal models
- Interaction with IGF binding proteins and the availability of free IGF in vitro
- Feedback effects on the somatotropic axis, including growth hormone and endogenous IGF-I, in livestock
- Amyloid pathology and cognition in transgenic mouse models of Alzheimer's disease
- Detection of the analog in seized products, for doping-control laboratories
Key findings
In female guinea pigs infused for 7 days, LR3 IGF-I increased the fractional weights of adrenals, gut, kidneys and spleen. Body weight gain and feed intake did not change significantly.
Conlon MA et al., J Endocrinol 1995In finisher pigs, a 4-day infusion of LR3 IGF-I decreased average daily gain, feed intake, plasma insulin, IGFBP-3 and endogenous IGF-I. Mean growth hormone fell 23% and the area under growth hormone peaks fell 60%.
Dunaiski V et al., J Endocrinol 1997In male 5XFAD mice treated intranasally from 3 to 10 months of age, LR3 IGF-1 reduced filamentous amyloid plaques in cortex. It did not preserve performance on behaviour and memory assays.
Engel MG et al., J Alzheimers Dis 2025Analysis of an injection vial from the black market identified His-tagged Long-R3-IGF-I, a form normally made for biochemical studies. Its effects in humans have not been described.
Kohler M et al., Growth Horm IGF Res 2010
What the studies measured
Study durations
- Guinea pig infusion study: 7 days of continuous infusion (Conlon 1995).
- Finisher pig infusion study: 4 days (Dunaiski 1997).
- Mouse Alzheimer model: 7 months of intranasal treatment, from 3 to 10 months of age (Engel 2025).
Endpoints
- Fractional organ weights and carcass composition
- Plasma IGF-I, IGF-II and IGFBP-3 concentrations
- Average daily gain and feed conversion efficiency
- Mean growth hormone concentration and area under growth hormone peaks
- Amyloid-beta plaque profile and behavioural memory testing
How strong is the evidence?
There are no published human clinical trials of Long R3 IGF-I, and the animal results are not uniformly anabolic, with growth suppressed rather than increased in pigs.
Common questions
Is IGF-1 LR3 an approved medicine?
Research compound. Not approved as a medicine by the FDA or the EMA. Some are registered in individual countries. Supplied for laboratory research only.
How much human research is there on IGF-1 LR3?
There are no published human clinical trials of Long R3 IGF-I, and the animal results are not uniformly anabolic, with growth suppressed rather than increased in pigs.
Does UU supply IGF-1 LR3?
Yes, as premium-grade research material for laboratory use. Every batch is tested by an independent lab and the certificate of analysis is published.