Because growth hormone levels decrease with age, ibutamoren has been touted as a fountain of youth due to its ability to increase growth hormone secretion in older adults. The hope for ibutamoren and other growth hormone secretagogues (a substance that stimulates hormone secretion) is that they would also increase muscle and reduce visceral fat. However, besides the changes in biomarkers, there has not been evidence of functional benefits with this ingredient.^[1]

Ibutamoren may be beneficial for growth hormone deficiency and has been designated as an orphan drug (meaning the drug is allowed to be studied for a rare disease but is not yet approved) for growth hormone deficiency by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA).^[2][3] Ibutamoren may have modest metabolic benefits. For example, a randomized controlled trial in older adults without known health conditions taking 25 mg of ibutamoren daily for 12 months showed a slight decrease in LDL cholesterol (−5.4 mg/dL) and a small increase in fat free mass (+1.1 kg) compared to taking a placebo. However, neither strength nor physical function were improved, and the small metabolic benefits did not last after ibutamoren was stopped.^[4] A randomized study of older adults recovering from hip fractures showed that taking 25 mg of ibutamoren daily for 24 weeks resulted in a slightly improved gait speed but did not improve any other measures of functional performance compared to a placebo.^[5] There is also interest in ibutamoren for improving bone mass, but there’s no evidence to support this effect in people without growth hormone deficiency.^[6]

Common side effects reported with 25 mg of ibutamoren taken by mouth daily include increased blood sugar (+5–10%), decreased insulin sensitivity, and increased appetite. Other reported side effects include muscle pain and mild swelling of lower extremities, which usually diminish with regular intake of ibutamoren.^[4][5][7] Additionally, there were some reports of transient elevations in liver enzymes ALT and AST.^[7] There were rare reports of hypertension and episodes of moderate heart failure in adults over 80 taking ibutamoren.^[5] These safety issues resulted in the termination of clinical research with ibutamoren in older adults.

Ibutamoren is a synthetic nonpeptide compound, referred to as a ghrelin mimetic, that activates L-type calcium channels, which leads to intracellular calcium increases and activation of protein kinase C (an enzyme that controls the function of various proteins). Ibutamoren interacts with growth hormone-releasing hormone (GHRH) and stimulates the release of growth hormone and insulin-like growth factor-1 (IGF-1). This can increase hunger and also reduce nitrogen wasting during energy restriction. Nitrogen wasting occurs when proteins (e.g., in muscles) are broken down into amino acids for energy and then removed from the body usually via urine.^[8] Reduced nitrogen wasting is thought to be how ibutamoren increases fat-free mass.