IGF1-LR3: Long R3 IGF-I Analogue Research Guide (2026)
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Introduction (research-only scope)
IGF1-LR3, usually written Long R3 IGF-I, is an engineered analogue of insulin-like growth factor I designed to evade the binding proteins that normally sequester IGF-I in tissue and serum. It is one of the most widely used growth factors in industrial cell culture, and that is the context in which most laboratories encounter it. This guide covers the structure, the mechanism and the regulatory position.
Research use only. The material described here is a laboratory reagent for in-vitro research by qualified professionals. It is not a medicine, supplement, cosmetic ingredient or veterinary product, is not for human or animal use, and nothing on this page is medical advice or a claim of effect in any person.
What is IGF1-LR3?
The analogue carries two modifications relative to human IGF-I: arginine replaces glutamate at position 3, and a 13-amino-acid extension (Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn) is added at the N-terminus, giving a molecular mass of 9117.50 (CAS 946870-92-4). Those two changes were described in the comparative work published in the Journal of Endocrinology in 1993. Peptra Labs supplies it as a lyophilised research reagent, 1 mg per vial.
How the reported mechanism works
Reduced binding-protein affinity
Native IGF-I is largely bound by IGF-binding proteins, which limits how much is free to engage the IGF-1 receptor. The Long R3 modifications lower that affinity substantially, so more of the added protein remains available in a culture system, which is why it is potent at lower concentrations than native IGF-I in cell work.
Same receptor, different availability
The analogue still signals through the IGF-1 receptor; what changes is availability, not the pathway. In a well-designed experiment the two are therefore not interchangeable controls.
What the published evidence covers
The literature is largely methodological: comparative potency studies in cell systems and extensive use as a serum-free medium supplement in biotechnology. It has no clinical development programme of its own. That makes it one of the few compounds here where the laboratory use case is the primary and legitimate one, provided the material is what the label says.
How to verify a IGF1-LR3 research peptide is real and pure
Two tests answer two different questions: mass spectrometry confirms identity (expected molecular mass 9117.50), HPLC quantifies purity. Our specification is at least 98%. Check the batch number printed on your vial against the lab reports archive: where a batch has been tested, its report is published there and links to the testing laboratory’s own verification page. If your batch is not listed yet, ask us for its documentation before use; a “typical” certificate is not evidence for a specific vial. See how to read a certificate of analysis.
Storage and reconstitution
Store the lyophilised material sealed, dry and protected from light at 2 to 8 °C for routine laboratory use, colder for long-term archiving. After reconstitution with bacteriostatic water, keep refrigerated and use within the window your protocol defines; repeated freeze-thaw cycles degrade peptides. General handling for all our reagents is in the peptide storage protocol.
Regulatory status
IGF1-LR3 is not an authorised medicine anywhere. IGF-1 and its analogues are named on the WADA Prohibited List (section S2, growth factors and growth factor modulators), prohibited at all times; the live list is the binding reference. Research-grade material supplied here is not a medicine and is for in-vitro laboratory use only. The wider framework, including anti-doping status, is described in the peptide risk profile.
Why labs choose our IGF1-LR3
Batch-numbered vials, published reports where a batch has been tested, shipping from an EU warehouse with tracking (no customs inside the EU) and prices shown with VAT included. Product page: IGF1-LR3 1 mg. Country-by-country sourcing questions are covered in the buyer guide Buy IGF1-LR3 in Europe.
References
- Zhao X et al. Effects of insulin-like growth factor-I and its analogues on bovine hydrogen peroxide release by neutrophils and blastogenesis by mononuclear cells. J Endocrinol. 1993. PubMed 7508487
- Dominikowski A et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol. 2026. PubMed 42395176