IGF-1 LR3
Educational information only — not medical advice. Many listed compounds are not FDA-approved for human use. Consult a licensed clinician before starting, changing, or stopping any protocol.
Overview
IGF-1 LR3 (Long R3 IGF-1) is a synthetic, engineered version of insulin-like growth factor 1, a hormone the body produces largely in response to growth hormone. It differs from native IGF-1 by an arginine-for-glutamic-acid substitution at the third position and an extra 13 amino acids added to one end of the chain, giving it 83 amino acids in total versus 70 in the natural peptide.
The purpose of those changes is to weaken its binding to the IGF-binding proteins that normally sequester circulating IGF-1. With less of it bound up, more remains free and biologically active, which is why it is commonly described as longer-acting and more potent than native IGF-1.
Most of the supporting evidence comes from animal and laboratory studies. Human clinical data is limited, and IGF-1 LR3 is not approved by any major regulator for therapeutic use. It is often discussed in the context of muscle growth and recovery.
How it works
IGF-1 LR3 acts on the same IGF-1 receptor as native IGF-1, triggering the PI3K/Akt/mTOR signaling cascade that is central to protein synthesis, cell proliferation, and tissue growth. In preclinical work it has been studied for its role in activating muscle satellite cells and supporting the growth of various tissues.
Its distinguishing feature is pharmacokinetic rather than mechanistic: because it binds poorly to IGF-binding proteins, a larger fraction stays unbound and available to the receptor. Studies in animals reported that this analog retained superior potency relative to standard IGF-1. The precise effects and safety profile in humans are not established.
Reported benefits
- Support for muscle protein synthesis and lean-tissue growth (preclinical and anecdotal data)
- Faster recovery and cellular repair after training or injury
- Activation of muscle satellite cells linked to longer-term growth capacity (animal models)
These are reported and studied effects, not guaranteed outcomes.
Considerations & side effects
Because robust human trials are lacking, the long-term safety profile of IGF-1 LR3 is not well characterized. As a growth-promoting agent it raises theoretical concerns around effects on blood sugar (given IGF-1’s insulin-like activity), tissue overgrowth, and any pre-existing or undiagnosed tumors, since IGF signaling can influence cell proliferation. Commonly discussed side effects include hypoglycemia-like symptoms and injection-site reactions.
Product purity and labeling vary widely in the research-chemical market, and IGF-1 LR3 is banned in competitive sport. It is not a substitute for evaluation and treatment by a qualified clinician.
Frequently asked
What is IGF-1 LR3?
A synthetic, longer-acting analog of insulin-like growth factor 1 (IGF-1). It carries an arginine substitution at position three plus a 13-amino-acid extension on its N-terminus, which greatly reduces its binding to IGF-binding proteins and is commonly reported to make it more potent and longer-lasting than native IGF-1.
Is IGF-1 LR3 FDA-approved?
No. IGF-1 LR3 is not approved by the FDA or any major regulator for human therapeutic use. It is sold for research purposes only and is prohibited in competitive sport.
How is IGF-1 LR3 different from native IGF-1?
Its structural modifications lower its affinity for IGF-binding proteins, so more of it stays free and active in circulation. In animal studies this translated to greater potency compared with native IGF-1.
Is it banned in sport?
Yes. IGF-1 and its analogs, including Long R3 IGF-1, fall under the growth factor category prohibited by anti-doping authorities, and validated tests exist to detect them.
References
- Tomas FM, et al. Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. ↗
- Conlon MA, et al. Long R3 IGF-I infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig. ↗
- Mongongu C, et al. Detection of LongR3-IGF-I, Des(1-3)-IGF-I, and R3-IGF-I for antidoping purposes. ↗
Related compounds
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A synthetic growth-hormone-releasing peptide (ghrelin-receptor agonist) that stimulates pituitary GH secretion via a pathway distinct from GHRH. The original GHRP from which ipamorelin was later derived; typically pulsed subcutaneously, often stacked with a GHRH.