IGF-1 LR3What the studies show
An engineered IGF-1 that dodges the body's binding proteins. Built in Adelaide in 1992 as a cell-culture reagent, and that is still where its evidence lives.
5 min read · Animal and lab studies · Updated November 2026
In short
- Name
- IGF-1 LR3 (long R3 insulin-like growth factor-1) (sold by Progression Labs as IGF-1 LR3)
- Evidence
- Animal and lab studies
- Bottom line
- One defining cell-culture paper, rat experiments from the same laboratory, and decades of use as a cell-growth reagent; no human study of any kind, and the only human evidence for an IGF-1 belongs to mecasermin, a different molecule.
Before you read this
This guide explains what published studies found. That is all it is.
It is not medical advice and it is not instructions for using anything. Where a dose appears, we are reporting what a named study gave the people or animals in it — a fact about the study, not an instruction to you.
The compounds here are not approved by the FDA for use in people and are sold for laboratory research only. A study tells you what happened to the subjects in it; it does not tell you what would happen to you. Talk to a doctor first.
What it is
Insulin-like growth factor-1 is the 70-amino-acid hormone the liver makes in response to growth hormone, and it carries most of growth hormone's effects on bone and muscle. Almost all of it travels in the blood bound to carrier proteins, the IGF-binding proteins, which hold it in reserve and keep it from the receptor. IGF-1 LR3 is a version made in bacteria by a group in Adelaide, Australia, with two changes: the glutamate at position 3 swapped for arginine (the "R3"), and a 13-amino-acid tail added to the front, a leftover from the way the protein was produced (the "long") 1. Both changes sit in the part of the molecule the binding proteins grip. The result is an IGF-1 that the carrier proteins barely hold, so nearly all of it is free to act 1.
The studies below call this molecule IGF-1 LR3 (long R3 insulin-like growth factor-1). Progression Labs sells it as IGF-1 LR3; the guide uses the store's name and the papers use theirs.
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What the 1992 study found
The paper that defined the molecule, from Francis, Ballard and colleagues in 1992, compared several engineered IGF-1 variants side by side. LR3 bound the binding proteins far more weakly than natural IGF-1, bound the IGF-1 receptor slightly less well, and was several times more potent at stimulating protein synthesis in cultured rat muscle cells 1. The authors drew the conclusion the title states: the extra potency came from escaping the binding proteins, not from a better fit with the receptor. That is the whole mechanism, and it is a cell-culture finding.
Rats
The same Adelaide group tested the variants in animals. In rats whose growth had been suppressed with the steroid dexamethasone, natural IGF-1 and its engineered variants were all anabolic, and the variants that escaped the binding proteins were the more potent, producing more weight gain and nitrogen retention over the treatment period 2. These are short experiments in small, growth-suppressed animals, designed to compare molecules rather than to model any human use. They ranked the variants against each other over a short treatment period; none followed the animals afterward.
Where it is actually used
IGF-1 LR3's real career has been in biotechnology. Because it is not sequestered by the binding proteins that cells secrete into their own medium, it works at low concentrations as a replacement for insulin in serum-free culture of the Chinese hamster ovary cells used to manufacture antibody drugs, and a 2000 study found it supported growth and recombinant protein production in those cultures in place of insulin 3. The company that commercialised it, GroPep, supplied it for exactly that. It was never developed as a medicine.
The approved IGF-1 is a different molecule
There is an approved IGF-1, and it is not LR3. Mecasermin, marketed as Increlex, is natural-sequence human IGF-1 made in bacteria, approved by the U.S. Food and Drug Administration in 2005 for children with severe primary IGF-1 deficiency, a rare condition in which the body cannot respond to growth hormone 4. In the long-term study behind that approval, 76 such children grew at 2.8 cm a year before treatment and 8.0 cm a year in the first year on mecasermin, and low blood sugar was the main side effect, because IGF-1 acts like insulin at high free concentrations 5. That last point is the reason LR3's defining feature, more free hormone, is also its reason for concern: everything that is known about an IGF-1 with no binding-protein reserve comes from cells and rats.
There is no published study of IGF-1 LR3 in a human being, for any purpose. It is not an approved drug anywhere.
What these studies are, and aren't
Animal and lab studies. One defining cell-culture paper, rat experiments from the same laboratory, and decades of use as a cell-growth reagent; no human study of any kind, and the only human evidence for an IGF-1 belongs to mecasermin, a different molecule.
Sources
- 1Francis GL et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. Journal of Molecular Endocrinology, 1992.
- 2Tomas FM et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochemical Journal, 1992.
- 3Morris AE, Schmid J. Effects of insulin and LongR3 on serum-free Chinese hamster ovary cell cultures expressing two recombinant proteins. Biotechnology Progress, 2000.
- 4Increlex (mecasermin) prescribing information. FDA approval August 2005 for severe primary IGF-1 deficiency.
- 5Chernausek SD et al. Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity. Journal of Clinical Endocrinology & Metabolism, 2007.
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