IGF-1 LR3: how it works, research and risks
Clinical review pending
What is known about IGF-1 LR3: its mechanism, preclinical findings on muscle and tumor growth, and US approval status. A benefit in humans remains unestablished.
Whether IGF-1 LR3 improves muscle building or athletic performance has not been clinically established in humans. The results described come from cell and animal experiments. In a mouse study (2), the substance reduced cancer-related muscle loss but also accelerated tumor growth.
What is IGF-1 LR3?
IGF-1 LR3 (Long R3 IGF-1) is a chemically modified form of insulin-like growth factor 1. Compared with the original molecule, one amino acid has been replaced. The amino acid chain has also been extended at one end, called the N-terminus. This makes the substance bind less strongly to carrier proteins and remain active longer.
IGF-1 LR3 is widely sold as an additive for laboratory cell cultures. It is also used for muscle building and performance enhancement, although a benefit in humans has not been established. It is not an approved medicine.
Further reading: Insulin.
How does IGF-1 LR3 work?
IGF-1 LR3 activates the IGF-1 receptor (1). This triggers growth signals that promote the production of muscle proteins in cell and animal models, a process called muscle protein synthesis. The changes to the molecule are intended to keep it active in the body for longer.
In laboratory experiments, IGF-1 LR3 promoted the development of muscle cells into specialized cells, known as differentiation. In a mouse model of cancer-related muscle wasting, it limited muscle loss. At the same time, tumors grew faster. Strong IGF signaling can therefore also promote unwanted cell growth; this growth-promoting property is called a mitogenic effect. The cell and animal experiments offer clues about its mechanism, but do not establish corresponding effects in humans.
Is IGF-1 LR3 FDA-approved?
No. The US Food and Drug Administration has not approved IGF-1 LR3. It is offered as a research chemical and also used for performance enhancement. There is no approved status for individually prepared medicines containing IGF-1 LR3 either. This type of preparation is called compounding in the United States.
In sport, the World Anti-Doping Agency (WADA) prohibits IGF-1 and its analogues—related variants such as IGF-1 LR3—at all times, both in and out of competition.
What does the research show?
Findings so far come from preclinical research: cell and animal experiments before clinical testing in humans. In a mouse study (2), IGF-1 LR3 limited muscle loss in cancer cachexia, a cancer-related wasting condition that includes loss of muscle. At the same time, it accelerated tumor growth. Laboratory studies also show that IGF-1 LR3 stimulates muscle cell growth.
Human clinical trials supporting its use for muscle building or performance enhancement are lacking. Faster tumor growth in the mouse model is a specific warning signal from preclinical research. The observed effects on muscle cells and muscle loss therefore do not establish a benefit for humans.