Growth Hormone Secretagogue (GHS)
A growth hormone secretagogue is any compound that stimulates endogenous GH release, a class spanning GHRH analogues and ghrelin-mimetic agents acting at the GHS receptor.
Growth hormone secretagogue is a functional category rather than a chemical one, covering anything that makes the pituitary release its own hormone. It divides cleanly by receptor. GHRH analogues act at the GHRH receptor and amplify the physiological releasing signal. Ghrelin mimetics act at GHS-R1a, working partly by direct stimulation and partly by withdrawing somatostatin tone, and they include the growth hormone releasing peptides and non-peptide small molecules such as ibutamoren.
The class dates to work by Cyril Bowers on enkephalin-derived peptides that released growth hormone through a receptor distinct from the GHRH receptor, which led to orally active non-peptides and eventually to the identification of ghrelin. Its regulatory record is thin: macimorelin is approved only as a diagnostic, and anamorelin holds a national approval in Japan for cancer cachexia. The most informative human data are the two-year trial of MK-677 in older adults, which restored IGF-1 to young-adult concentrations and increased fat-free mass by roughly a kilogram without improving strength or function, while raising fasting glucose.
The pattern across the class is worth stating plainly: raising growth hormone and IGF-1 is easy and reproducible, and it is a surrogate. Improvement in strength, physical function or clinical outcome has repeatedly failed to follow.
Two framings mislead. The first is the marketing distinction between peptides and drugs, used to imply that unapproved secretagogues sit in a lighter regulatory category; research-use-only labelling is a statement about intended use, not a quality assurance. The second concerns sport, where athletes often assume only recombinant growth hormone is prohibited, when section S2 of the WADA Prohibited List covers releasing factors and secretagogues as a class.