IGF-LR3 stands for insulin-like growth factor-1 long R3. It is a synthetic form of insulin-like growth factor I (IGF-1), which is important to cell development and growth. IGF-LR3 is modified in two main ways, the first being through an extension of the amino acid chain. Additionally, the addition of R3 is a structural change that increases activity. As such, the half life is extended from minutes to up to 20 to 30 hours (1).
IGF-1 is a growth factor that modulates anabolic and catabolic processes in the skeletal muscle. It does so by increasing synthesis of skeletal muscle proteins via multiple biological pathways. It may also inhibit muscle atrophy and promote skeletal muscle regeneration (2).
IGF-1 is essential to the growth and development of many of the body’s tissues. When it comes to skeletal muscle, IGF-1 supports myoblast proliferation and differentiation as well as fiber formation. It can also increase muscle mass, promote regeneration post-injury, and increase skeletal muscle functional capacity.
IGF-1 has been evaluated in several human studies, including for conditions related to sarcopenia (a condition leading to loss of muscle mass), growth hormone deficiency, muscle wasting, diabetes, and neuromuscular disease. Results have indicated that IGF-1 can increase lean body mass when combined with growth hormone. It has also demonstrated enhanced fat loss, increased protein synthesis, and increased lean body mass (3).
IGF-1 has demonstrated effects in humans that have certain medical conditions related to low muscle mass and neuromuscular diseases. In these studies, it has shown demonstrated effects in increasing muscle-related parameters.
Because of these results, many individuals have tried extrapolating these effects to healthy individuals with IGF-LR3. IGF-LR3 is used to promote muscle growth and hypertrophy and enhance recovery and injury healing. However, it is important to note that this synthetic formulation is not FDA-approved nor has IGF-1 been approved in healthy individuals.
The FDA has approved a recombinant human IGF-1 (rhIGF-1) for the treatment of growth failure in pediatric patients (4). However, this is a different form of IGF-1 versus IGF-LR3. IGF-LR3 is not approved by the FDA and is instead available only as a research chemical. Thus, it does not abide by the same established safety and efficacy standards as approved medications.
Additionally, IGF-LR3 is not held to the same quality standards as approved drugs. Thus, it runs the risk of mislabeling, contamination, and dosing inconsistency.
Potential side effects include low blood sugar, tonsillar hypertrophy, and allergic reactions. There are also concerns related to IGF-1’s link to conditions such as intracranial hypertension, lymphoid tissue hypertrophy, malignant neoplasia, and more (4).
Although IGF-1 has established efficacy in certain muscular conditions, there is not much evidence available to support the use of IGF-LR3. It is not approved by the FDA and thus its benefit-risk profile is not well-established in humans.
The information provided in this article is for educational purposes only and is not intended as medical advice. Many peptides are not FDA-approved for human use outside of limited clinical contexts. These compounds are often obtained through unregulated sources that lack quality control. Studies suggest 30–65% of products may be contaminated or mislabeled, with risks including endotoxins, heavy metals, and incorrect sequences. At Weight Loss & Vitality, we focus on evidence-based, medically supervised therapies.
As of April 21, 2026, regulatory status for many peptides remains under review and may change as additional data and guidance become available.
With increasing interest in peptide therapies, having experienced clinical guidance is essential. Our expert-led peptide therapy services help patients navigate options safely and effectively.
References
https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/021839s033lbl.pdf
