IGF-1 LR3

What it is

Engineers built IGF-1 LR3 as an 83-amino-acid version of the human hormone insulin-like growth factor-1, a growth factor tied to cell growth and tissue development throughout the body. The modification adds extra amino acids at one end of the chain and changes a single position elsewhere, which together reduce how strongly the molecule binds to insulin-like growth factor binding proteins, the carrier proteins that normally hold the natural hormone in check.

Because it escapes that carrier-protein control, researchers report the modified molecule stays active in the bloodstream far longer than natural insulin-like growth factor-1, and animal work describes it as substantially more potent gram for gram. Nobody has ever put it through a clinical trial in people, and everything known about it comes from experiments run in animals and in cells.

How it is studied

All published research on IGF-1 LR3 is preclinical: studies in whole animals, mainly rats, pigs, and sheep, plus some laboratory work on isolated tissue. No human trial of any kind has been conducted or registered. The animal studies vary widely by species and by what was measured, from muscle growth in rats to blood sugar and growth hormone regulation in pigs and fetal sheep, which makes it difficult to generalize any single result across species, let alone to people.

What studies report

• A short infusion of IGF-1 LR3 into fetal sheep sharply reduced insulin release from the pancreas during the infusion, an effect that did not persist once the same pancreatic tissue was studied on its own outside the animal [2]. [2]
• In young pigs given IGF-1 LR3 daily for four days, growth actually slowed rather than sped up, and the animals ate less; the treatment also lowered several of the pigs' own growth-hormone-pathway hormones [3]. [3]

What is not known

There is no human clinical data on IGF-1 LR3 of any kind, so nothing in the published literature speaks to how it behaves in a person. The animal findings that are available point in inconsistent directions across species, slowing growth in pigs while other reports describe increased muscle mass in rats, which leaves open how much any single animal result can be generalized. Long-term effects, effects at different life stages, and any relationship to cancer risk from sustained growth-factor signaling have not been studied in a controlled trial in any species.

Reported adverse findings

• In the fetal sheep study, repeated infusion of IGF-1 LR3 over about a week was associated with the deaths of four animals from low blood sugar and low blood oxygen, along with a marked drop in circulating amino acids [2]. [2]

Regulatory status

No national medicines regulator has ever cleared IGF-1 LR3 for use in people. The World Anti-Doping Agency bans it for competitive athletes, grouping it with other growth-factor compounds. In the scientific record it exists solely as a laboratory tool used to study animals.