IGF-1 LR3
A long-acting analog of insulin-like growth factor 1; not FDA-approved.
What it is
IGF-1 LR3 is a lab-modified version of insulin-like growth factor 1, engineered to evade the binding proteins that normally restrain IGF-1 — making it substantially more potent in cell and animal experiments. It exists for laboratory research and was never developed as a human drug.
Its bodybuilding reputation rests on IGF-1's central role in growth signaling. The same biology is why the theoretical risk profile is serious: IGF-1 signaling is deeply entangled with cell proliferation, hypoglycemia is a known acute concern, and no human safety program has ever been run.
What researchers have actually studied it for
Cell growth and muscle physiology in laboratory and animal research; designed as a research reagent, never developed for humans.
How it works
Native IGF-1 with an arginine substitution and a 13-amino-acid extension that together wreck its binding-protein affinity — so instead of circulating 98% sequestered, it stays free and active. In the lab that means prolonged, amplified IGF-1 receptor signaling: growth, glucose uptake, proliferation.
Where it came from
Created in the 1990s as a cell-culture reagent — media suppliers needed IGF-1 that binding proteins wouldn't soak up. Native IGF-1 (mecasermin) did become a niche approved drug for severe IGF-1 deficiency; the LR3 lab variant never entered human development but escaped into physique-culture folklore.
What the research record actually contains
- Extensive laboratory use as a cell-growth reagent — its actual purpose.
- Animal growth studies.
- Zero human trials of any kind; the approved cousin mecasermin's clinical file (hypoglycemia warnings included) is the nearest human signal.
What's known about risks
Acutely, IGF-1 signaling drives glucose down — mecasermin's label carries serious hypoglycemia warnings, and LR3's binding-protein escape plausibly sharpens that. Chronically, unrestrained proliferative signaling is the theoretical cancer-risk conversation nobody has data to close. No human file exists.
Where it stands legally
A research reagent, never approved for human use anywhere; prohibited in tested sport as an IGF-1 analog.
Worth asking a licensed provider
- 1.Do I understand this is a cell-culture reagent with zero human trials?
- 2.If muscle growth is the goal, what does my training, protein intake and recovery picture look like first?
- 3.Am I subject to any testing regime where IGF-1 analogs end careers?