IGF-1 LR3: What It Is and What the Research Shows

At a glance

What is IGF-1 LR3?

IGF-1 LR3 (Long R3 IGF-1) is a chemically modified version of insulin-like growth factor-1 with an amino-acid substitution and an added N-terminal extension. These changes lower its binding to carrier proteins and extend its activity, and it is widely sold as a laboratory cell-culture supplement. In the performance market it is used as a muscle-growth drug; it is not an approved medicine.

How does it work?

IGF-1 LR3 activates the IGF-1 receptor, driving the growth signaling that promotes muscle protein synthesis in cell and animal models. Its modifications are proposed to prolong its activity in the body. In laboratory work it increased muscle-cell differentiation, and in a mouse model of cancer-related muscle wasting it limited muscle loss, but at the cost of accelerated tumor growth, illustrating the mitogenic (growth-promoting) concern that comes with strong IGF signaling. These are animal and cell findings. This describes the proposed mechanism, separate from proven outcomes in people.

Is it FDA-approved?

No. IGF-1 LR3 is not approved by the FDA; it is a research chemical and performance-enhancing drug with no approved compounding status. In sport, IGF-1 and its analogs are prohibited at all times under the WADA list.

What does the research show?

The evidence is preclinical. According to PubMed, a mouse study found IGF-1 LR3 limited muscle loss in cancer cachexia but accelerated tumor growth, and laboratory assays show it stimulates muscle-cell growth. There are no human clinical trials supporting muscle or performance use, and the tumor-growth signal is a specific preclinical concern. Its marketed benefit is unproven in people.

Evidence strength

Low research: There is no human efficacy evidence; the anabolic rationale rests on animal and cell studies, which also include an explicit tumor-growth signal.

Sources: a mouse study of IGF-1 LR3 in muscle wasting and tumor growth (Levolger et al., Scientific Reports, 2019, DOI: 10.1038/s41598-019-46178-9) and a review of performance peptides (Dominikowski et al., Frontiers in Endocrinology, 2026, DOI: 10.3389/fendo.2026.1822475), indexed on PubMed; and the WADA Prohibited List. This document is educational, is not medical advice or a health claim, and is not an offer to sell any product.