Ipamorelin

What it is

Ipamorelin belongs to a group of lab made molecules called growth hormone releasing peptides. Its five amino acid building blocks, in order, are alpha-aminoisobutyric acid, histidine, a mirror-image (D-form) 2-naphthylalanine, a mirror-image phenylalanine, and lysine, with the chain ending in an amide cap; researchers put its molecular weight at close to 712 daltons. It is described as binding the same receptor that ghrelin, the body's own natural hunger signal, uses to reach the pituitary gland.

What sets ipamorelin apart from earlier growth hormone releasing peptides is its reported selectivity. Where some earlier compounds in this group also raised cortisol and prolactin, the compound's original laboratory report describes its effect on those two hormones as minimal. That's the main reason it draws research attention, mostly tied to growth hormone and, in one trial, to gut movement after surgery.

How it is studied

The earliest work on ipamorelin was done in rat and pig tissue and in live rats and pigs, comparing how strongly it released growth hormone against an older peptide in the same family, and checking whether it also raised cortisol and prolactin the way that older peptide did [1]. In humans, one trial gave eight healthy men at a time rising amounts of ipamorelin through a vein over 15 minutes, then tracked blood levels of the peptide and of growth hormone to see how quickly the compound cleared and how it triggered hormone release [2]. A separate multi-center trial gave ipamorelin twice a day by vein to patients recovering from bowel surgery, to see whether it helped them tolerate solid food sooner [3]. No study located for this entry tested ipamorelin for exercise recovery, sleep, or extended everyday use in humans.

What studies report

• In the original laboratory report, ipamorelin released growth hormone from pituitary cells and in live rats and pigs about as strongly as an older, related peptide, but without raising cortisol or prolactin the way that older peptide did. [1]
• In the human trial with rising amounts given through a vein, ipamorelin left the blood quickly, with a half-life (the time for half of it to clear) of about two hours. [2]
• That same human trial found each amount of ipamorelin triggered a single short burst of growth hormone release that faded within a few hours, rather than a sustained rise. [2]
• In the bowel surgery trial, side effects occurred at a similar rate in the ipamorelin and placebo groups, and the trial's authors described ipamorelin as well tolerated over the week it was given, though patients did not return to a solid meal significantly faster than those on placebo. [3]

What is not known

No study located for this entry tested ipamorelin for exercise recovery or sleep in humans, so claims about faster recovery or better sleep that circulate about this peptide are not backed by a published trial and are not repeated here. The one controlled human trial that tested a health outcome, recovery after bowel surgery, did not find a benefit over placebo on its main measure. It is not known whether ipamorelin affects growth hormone or body composition in healthy adults using it outside a hospital setting, since no such trial was found. Long-term human safety data beyond the one-week surgery trial has not been published in a form this review could locate.

Reported adverse findings

• In the bowel surgery trial, most participants in both the ipamorelin group and the placebo group reported at least one side effect during the week of treatment, so the trial could not separate side effects caused by ipamorelin from those caused by the surgery itself. [3]

Regulatory status

Neither the United States Food and Drug Administration nor Health Canada has approved Ipamorelin for any human or animal purpose. The scientific literature reviewed here treats it purely as a compound for laboratory study.