A modified, longer-acting analog of insulin-like growth factor 1 (IGF-1) sold as a research chemical. It is characterized mainly as a laboratory cell-culture reagent, with no human trials for muscle or performance use.
Reviewed for accuracy · Last reviewed July 8, 2026IGF-1 LR3 (Long R3 IGF-1) is a synthetic analog of the hormone IGF-1. It adds a 13-amino-acid N-terminal extension and swaps arginine for glutamic acid at position 3, changes that sharply reduce its binding to the IGF-binding proteins that normally sequester IGF-1. The practical effect studied in the lab is more free, longer-acting analog and greater potency in cell culture. It is documented and sold primarily as a cell-culture supplement and research reagent, and it is used anecdotally in bodybuilding. It is not FDA-approved, and there are no human clinical trials of the LR3 analog for muscle, performance, or any therapeutic use, so its efficacy and safety in people are uncharacterized.
It is important not to confuse IGF-1 LR3 with mecasermin, which is recombinant human IGF-1 (the native sequence) approved for a rare pediatric growth disorder, severe primary IGF-1 deficiency. That is a different molecule with a narrow, specific indication, and its approval says nothing about the IGF-1 LR3 research chemical. One further caution runs through all IGF-1 signaling: the IGF-1 receptor pathway has been reviewed as involved in tumour transformation and the survival of malignant cells, so any agent that amplifies IGF-1 signaling carries a theoretical proliferative or cancer-growth concern. That is a concern about the pathway, not a demonstration that IGF-1 LR3 causes cancer in people, which has not been studied.
There is no validated human dose. IGF-1 LR3 has no human trials and no approved label, so any injection figures circulating online are anecdotal and clinically unvalidated.
Read the full IGF-1 LR3 dosage guide →Human safety is uncharacterized. Because IGF-1 lowers blood sugar, hypoglycemia is a recognized risk, and amplified IGF-1 signaling carries a theoretical proliferative or cancer-growth concern.
Read the full IGF-1 LR3 side effects guide →Peptide analogs like this are generally kept refrigerated, with unmixed material away from light, and reconstituted material used within a short window. Because it is a research reagent, follow the supplier's handling data. See the full storage & safety guide for handling and disposal basics.
This page is an independent educational reference and is not medical advice, and does not indicate any approval status for any use. IGF-1 LR3 is a research chemical with no human trials. Talk to a doctor before considering any compound.