Kisspeptin

Kisspeptin sits at the very top of the reproductive hormone chain, acting on KISS1R receptors on the brain's GnRH neurons — the master switches for reproduction.

When it stimulates those neurons it triggers the natural pulse of GnRH, which drives the pituitary to release LH and FSH, which then signal the ovaries or testes to make sex hormones and eggs or sperm. Because it works through this natural cascade rather than overriding it, researchers have explored it as a gentler ovulation trigger in fertility care and as a probe of hypothalamic function.

It's short-acting and still investigational, studied by IV and subcutaneous routes. A key appeal is that triggering ovulation through the physiologic pathway may carry a lower risk of ovarian hyperstimulation than the standard hCG trigger.