Sermorelin

Sermorelin is the shortest active fragment of GHRH — just the first 29 amino acids — and it does the same basic job: it tells the pituitary to release the body's own growth hormone.

When it binds the pituitary's GHRH receptors it triggers a burst of GH while leaving the natural pulse-and-feedback system intact. That preserved physiology is part of why it was historically used as a diagnostic: give sermorelin, then measure the GH response to gauge how much reserve the pituitary has.

Its half-life is only minutes, so any effect is brief, and its use depends on that short, sharp stimulus. Its commercial availability has come and gone over the years, and the GH response can be blunted by the body's opposing hormone, somatostatin.