IGF-1 LR3

Insulin-like growth factor-1 (IGF-1) is a 70-amino-acid hormone, made mainly in the liver in response to growth hormone, that drives growth and tissue building. Most IGF-1 in the blood is bound to IGF-binding proteins (IGFBPs), which limit how much reaches tissues. IGF-1 LR3 is an engineered version with two changes: the glutamic acid at position 3 is replaced by arginine, and an extension peptide derived from the first 11 amino acids of porcine growth hormone is attached to the start of the chain ^[1]. It is much larger than most peptides discussed on this site.

The analogue was made by researchers in Adelaide, Australia, who also studied the truncated analogue des(1-3)IGF-I, as a tool to separate the effects of receptor binding from binding-protein interactions ^[1]. It is used as a laboratory reagent ^[6]. It is also sold by research peptide vendors and on the black market as a body-composition drug, which is a use that has never been tested in controlled human studies. It is related in purpose, though not in mechanism, to growth hormone secretagogues such as CJC-1295 and ipamorelin.

IGF-1 LR3 acts on the same type 1 IGF receptor as native IGF-1, and can also act through the insulin receptor. Its main difference is that it binds IGFBPs very weakly. In cell lines that secrete these binding proteins, it was more potent than native IGF-1 at stimulating protein and DNA synthesis and at inhibiting protein breakdown; in cells that do not secrete binding proteins, it was actually less potent than IGF-1 ^[1]. It binds the type 1 IGF receptor about three times less well than IGF-1, yet in rats it was about 2.5 times more potent, which the researchers attributed to its escape from binding proteins ^[2].

Because it is not held in reserve by binding proteins, its effects in animals are stronger and longer-lasting than native IGF-1, including its insulin-like effect of lowering blood glucose ^[3].

In rats made catabolic with the steroid dexamethasone, infused IGF-1 LR3 and des(1-3)IGF-I were about 2.5-fold more potent than IGF-1 at improving weight gain and nitrogen retention, and all of the IGF peptides markedly increased gut weight ^[2]. In food-restricted rats, a week-long infusion helped maintain body weight and nitrogen balance but did not preserve muscle protein; in adult rats it increased muscle protein breakdown and reduced protein synthesis ^[4]. The author concluded it did not prevent loss of lean tissue during food restriction.

In pigs, IGF-1 LR3 and related analogues lowered blood glucose two to three times more potently than IGF-1 and kept it suppressed for longer, with roughly a four- to eight-fold greater cumulative hypoglycaemic effect over four hours ^[3]. In mdx mice, a model of Duchenne muscular dystrophy, four weeks of continuous IGF-1 LR3 reduced muscle damage from lengthening contractions ^[5].

These studies were designed to understand IGF biology in animals. None tested whether IGF-1 LR3 builds muscle or reduces fat in healthy people.

We found no published clinical trials of IGF-1 LR3 in humans. Evidence about human use comes from anti-doping and forensic work: one analysis of a black-market injection vial found IGF-1 LR3 carrying a “His-tag”, a purification label typically used in laboratory reagents, whose effects in humans have never been described ^[6]. A 2026 clinical review grouped IGF-1 LR3 with other unregulated growth-hormone-axis compounds and listed reported adverse effects across the class, including blood-sugar disturbances, fluid retention and joint and muscle pain ^[8].

All published doses are from animals. Examples include continuous infusion of about 98 nmol per kg per day in rats ^[4], bolus injections of 20 and 50 µg/kg in pigs ^[3], around 1.5 mg/kg per day by osmotic pump in mice ^[5], and a single 100 µg/kg intramuscular dose in rats for detection testing ^[7]. No human dose has been established, and animal doses cannot simply be converted to human doses.

The best-documented effect in animals is low blood sugar (hypoglycaemia), which was more potent and more prolonged than with native IGF-1 ^[3]. IGF-1 signalling also promotes cell growth, and a recent review described mitogenic (growth-promoting) concerns about IGF-1 analogues as biologically plausible but unproven ^[8]. There are no controlled human safety data. Black-market products have been found to contain unexpected variants and oxidised or degraded forms, so the content of any vial cannot be assumed ^[6][7].

IGF-1 LR3 is not approved as a medicine anywhere. It is different from mecasermin, the licensed recombinant form of native human IGF-1 used for severe primary IGF-1 deficiency in children. For sport, exogenous IGF-1 is prohibited at all times under the World Anti-Doping Agency (WADA) Prohibited List, and anti-doping laboratories describe IGF-1 analogues including LongR3-IGF-I as prohibited substances ^[7]. See our legal status overview for country-level rules.

IGF-1 LR3 is usually supplied as a freeze-dried powder. Anti-doping laboratories found abundant oxidised forms in black-market samples, a sign that product quality and degradation are real concerns ^[7]. General guidance is in our peptide storage guide.

Identity testing matters more than usual for IGF-1 LR3 because it is a larger molecule with known variants, such as His-tagged forms, turning up in black-market products. You can compare prices, learn how to read a COA, and see our list of third-party tested suppliers.