A minor constituent of opium, thebaine or paramorphine (C₁₉H₂₁NO₃) is chemically similar to both morphine and codeine, but produces stimulatory rather than depressant effects. Thebaine is not used therapeutically, but is converted into a variety of compounds including codeine, hydrocodone, hydromorphone, oxycodone, oxymorphone, nalbuphine , naloxone, naltrexone, buprenorphine and etorphine . It is controlled in Schedule II of the Controlled Substances Act as well as under international law. Another, more mysterious analogue of thebaine, called thebacon, is also scheduled or illegal in many countries, although there is no record of it having existed otherwise.

Thebaine is listed as a Class A drug under the 1971 Misuse of Drugs Act in the United Kingdom.