IGF-1 LR3
A modified analogue of insulin-like growth factor 1 (IGF-1) engineered to last much longer and resist binding proteins, giving it strong, sustained activity. It is a research / performance compound — not an approved drug — and is banned in sport.
Quick take
- What it is: a lab-modified, long-acting version of insulin-like growth factor 1 (IGF-1) that resists the binding proteins which normally limit IGF-1.
- What people use it for: muscle growth and recovery, based on IGF-1’s anabolic effects.
- What we actually know: it is potent in cell culture; there is essentially no controlled human data for the performance uses, and it carries real metabolic risks.
- Status: a research / performance compound, not FDA-approved, and prohibited in sport.
What it is
IGF-1 LR3, or Long R3 IGF-1, is a modified analogue of insulin-like growth factor 1 (IGF-1). It carries two engineered changes: an arginine substitution at position 3 and an added N-terminal peptide extension. Together these make it resist the IGF-binding proteins that normally hold natural IGF-1 in check, and give it a substantially longer half-life — so it stays active far longer and more freely than native IGF-1.1
It was originally developed as a research reagent to drive cell proliferation in culture. Its appearance as a “performance” compound is an off-label, unapproved extension of that.
How it works
IGF-1 is a central anabolic signal — it promotes cell growth, protein synthesis and survival, and contributes to muscle growth and repair.1,2 By dodging the binding proteins that normally limit how much free IGF-1 is available, IGF-1 LR3 produces a stronger, more sustained IGF-1 signal than the body’s own version. That same potency is the source of both its appeal and its risk.
What the evidence shows
Cell & animal studies
IGF-1 LR3 is well established as a potent growth driver in cell culture, which is its original purpose, and animal work confirms strong IGF-1-type activity.2
Human studies
Controlled human trials of IGF-1 LR3 for muscle growth or recovery are essentially absent. The performance claims rest on IGF-1’s known biology and on anecdote, not on demonstrated, safe benefit in people.3 This gap matters especially because the compound’s sustained, binding-protein-resistant activity carries real metabolic consequences.
Dosages reported in the literature
Informational only. The figures below describe doses reported informally rather than in controlled human trials. They are not a recommendation or a prescription, and appropriate use, if any, should be determined by a qualified healthcare professional who can account for your individual situation.
| Setting | Route | Reported range |
|---|---|---|
| Cell / animal research | Various | Not directly applicable to humans |
| Anecdotal (performance) | Subcutaneous / intramuscular | Reported in microgram amounts; protocols vary widely |
Because there are no dose-finding human trials for these uses, no range here should be read as established as safe or effective.
Safety & side effects
The most concrete risk is hypoglycaemia (low blood sugar), because IGF-1 shares activity with insulin signalling and IGF-1 LR3 is potent and long-acting.3 More broadly, sustained, unregulated stimulation of a powerful growth pathway raises theoretical concerns about abnormal tissue growth, which is a recognised caution for IGF-1-type compounds in the absence of controlled human safety data. There is essentially no long-term human safety information.
As with all peptides from the unregulated market, product purity, identity and dose accuracy vary between sources.
Legal & regulatory status
IGF-1 LR3 is not approved by the FDA for any use and is best described as a research reagent and unapproved performance compound. IGF-1 and its analogues are prohibited in sport at all times by the World Anti-Doping Agency (category S2, peptide hormones, growth factors and related substances).4 Rules vary by country and change over time.
References
- Tomas FM, Lemmey AB, Read LC, Ballard FJ. Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. Journal of Endocrinology. 1996;150(1):77-84. [PMID 8708565, doi:10.1677/joe.0.1500077]
- Barclay RD, Burd NA, Tyler C, Tillin NA, Mackenzie RW. The Role of the IGF-1 Signaling Cascade in Muscle Protein Synthesis and Anabolic Resistance in Aging Skeletal Muscle. Frontiers in Nutrition. 2019;6:146. [PMID 31552262, doi:10.3389/fnut.2019.00146]
- Nwabo Kamdje AH, Seke Etet PF, Kipanyula MJ, Vecchio L, Tagne Simo R, Njamnshi AK, Lukong KE, Mimche PN. Insulin-like growth factor-1 signaling in the tumor microenvironment: Carcinogenesis, cancer drug resistance, and therapeutic potential. Frontiers in Endocrinology. 2022;13:927390. [PMID 36017326, doi:10.3389/fendo.2022.927390]
- World Anti-Doping Agency. The Prohibited List (2026), Section S2: Peptide Hormones, Growth Factors, Related Substances and Mimetics — includes Insulin-like growth factor-1 (IGF-1) and its analogues, prohibited at all times. [wada-ama.org]