Heroin

Pleasure: the reward centre

The pleasant feelings from heroin arise because the reward centre is stimulated. The key neurotransmitter in the reward system is dopamine.

If you take heroin, your body first converts the drug into morphine. Morphine mimics, or basically performs the same actions, as endorphins, the natural neurotransmitters.

That means that bodily processes involving endorphins are imitated when you take heroin.