Ibutamoren, also known as MK-677 or Nutrobal, is a substance that increases the body's Human Growth Hormone (HGH) levels. It's a selective agonist of the ghrelin receptor, mimicking the growth hormone-stimulating effects of the hormone ghrelin, which is secreted in response to hunger. Ibutamoren increases the release of endogenous GH in adults and children with GHD.

GH secretagogues such as MK-677 (ibutamoren mesylate)7 stimulate the release of GH in the anterior pituitary and produce a rapid and robust upregulation of circulating IGF-1 levels.