Where to Buy IGF-1 LR3: Vendor Comparison, Benefits & Side Effects

IGF-1 LR3 (Long R3 IGF-1) is an engineered analogue of human insulin-like growth factor 1: arginine replaces glutamic acid at position 3, plus a 13-residue N-terminal extension, both changes weakening its grip on the binding proteins that normally sequester IGF-1. It is sold strictly as a research chemical, is not approved by the FDA or any other regulator for human use, and nothing here is medical advice.

Its documented use is in the laboratory, as a serum-free supplement for cell culture; the animal work specific to it is largely rat growth studies from the early 1990s. Recombinant native IGF-1 (mecasermin) is an approved medicine for severe primary IGF-1 deficiency, but LR3 is a different molecule with no controlled human trials of its own.

PeptidesFinder's role is narrower than the science. We track which research vendors list IGF-1 LR3, normalise every listing to a price per milligram so vial sizes can be compared, and record whether a recent certificate of analysis is on file. The comparison below is re-checked on a schedule; confirm current pricing on the vendor's own site before ordering.

What follows comes from receptor pharmacology, cell-culture work and rodent studies. Where a result was produced with native IGF-1 rather than the LR3 analogue it is said so explicitly, because the two are routinely conflated.

Receptor target. IGF-1 LR3 acts at the type 1 IGF receptor (IGF-1R), a receptor tyrosine kinase; ligand binding drives autophosphorylation of the beta subunits and recruitment of the adaptor proteins IRS-1 and Shc. In binding studies it also engages the insulin receptor and IR/IGF-1R hybrid receptors with lower affinity, which is the usual explanation for the fall in blood glucose observed when IGF-1 analogues are given to laboratory animals.

Escape from the binding proteins. Native IGF-1 circulates almost entirely bound to a family of six IGF binding proteins, which limits how much of it reaches the receptor. The arginine-for-glutamate swap at position 3 and the N-terminal extension both reduce IGFBP affinity, and in the binding and cell-based potency assays reported by Francis and colleagues the analogues that evade IGFBP capture were substantially more potent than native IGF-1 at the same receptor. The difference is attributed to ligand availability, not to a different receptor or a different signal.

Downstream signalling. Activated IGF-1R feeds two well-characterised branches: PI3K-Akt-mTOR, associated in cultured cells with protein synthesis and suppression of apoptosis, and Ras-Raf-MEK-ERK, associated with proliferation. In cultured myoblasts these are the routes by which IGF-1 promotes differentiation and myotube hypertrophy. That is cell-culture pharmacology, not a human finding.

Rodent evidence. The in vivo work specific to this analogue is a cluster of rat studies from the early 1990s, reporting greater weight gain, nitrogen retention and gut and muscle protein accretion than equivalent native IGF-1 in both normally fed and catabolic rats. The endpoints were carcass and nitrogen-balance measurements in rats, and there is no human counterpart to any of it. The frequently cited demonstrations of skeletal-muscle hypertrophy, in IGF-1 transgenic mice and in mouse muscle given IGF-1 by viral delivery, used native IGF-1 and not LR3, so reading them onto this analogue is an inference from shared receptor biology rather than a result about it.

Documented laboratory use. The one setting in which the analogue itself has a reproducible published role is cell culture: LONG R3 IGF-I is used as an insulin or serum substitute in serum-free mammalian production lines, where it has been reported to support the growth and protein productivity of CHO cells. That is a bioprocessing reagent application, and it is what research-grade material is nominally sold for.

None of this establishes safety or efficacy in humans, and the mitogenic, anti-apoptotic character of IGF-1R signalling is itself a reason the compound stays in the laboratory: observational studies have linked higher circulating IGF-1 to the incidence of several cancers, an association in population data rather than a demonstrated effect of this analogue. Recombinant native IGF-1 (mecasermin) is an approved drug for severe primary IGF-1 deficiency, but IGF-1 LR3 is a different, modified molecule, and the research-grade product sold by these vendors is not that approved medicine and is not approved for any medical use.