Kisspeptin

Hypothalamic neuropeptide that triggers GnRH release — restores natural sex-hormone signaling upstream.

Kisspeptin sits at the very top of the hormone chain — it's the signal that tells your brain to kick off the whole cascade that ends in testosterone (or estrogen) production. Instead of replacing a hormone, it restarts your own factory from upstream, which is why it's used to restore natural testosterone, support fertility, and recover the HPG axis after it's been suppressed (e.g., post-cycle). It also lifts libido without the melanocortin side effects of the tanning peptides — a cleaner "switch the system back on" approach.