Opiate

Opiates are a class of drugs that are derivatives (in the broadest sense of the word) of opium. These include two groups of alkaloids: phenanthrenes and papaverines. Opiates in the narrower sense of the word are only the phenanthrenes. Opioids are synthetic drugs that are chemically unrelated to the opiates, but act on the same receptors in the central nervous system and have similar clinical effects.

Phenanthrenes:

Naturally occurring in opium:

Semisynthetic derivatives:

Fully synthetic:

Phenylheptylamines:

Methadone
levomethadyl acetate hydrochloride (LAAM)

Phenylpiperidines:

Meperidine
Fentanyl
Alfentanil
Sufentanil
Remifentanil

Veterinary:

Etorphine
Carfentanyl

A high number of opiates are considered to be highly addictive. One exception is loperamide, which cannot cross the blood-brain barrier.