Endorphin
From Memory Alpha, the free Star Trek reference.
Endorphins are nature's painkillers, produced in the pituitary gland and hypothalamus of all humanoid vertebrates. They regulate pain and hunger and are connected to the production of sex hormones.
The Cardassian Obsidian Order provided its operatives with cranial implants that stimulated the production of endorphins, thus allowing the wearer to resist torture. (DS9: "The Wire")
