Opiates (from Opium) are the constituents or derivatives of constituents found in opium, which is processed from the latex sap of the opium poppy, Papaver somniferum. The major biologically active opiates found in opium are morphine, codeine, thebaine and papaverine. Synthetic opioids such as heroin and hydrocodone are derived from these substances, especially morphine, codeine, and thebaine. Noscapine, narceine and more than 25 other alkaloids are also present in opium, but have almost no effect at all on the human central nervous system (CNS), and are normally not considered as opiates.

Opiates belong to the large biosynthetic group of benzylisoquinoline alkaloids.