As members of the same class of drugs, al l opioids are similar in chemical nature. These chemicals may be derived naturally from the opium plant or synthesized in the laboratory. The different types of opioids include:

Naturally occurring opioids

These are alkaloids that are present in the resin of the poppy or opium bulbs and include morphine, codeine and thebaine. Natural opioids may also occur in the leaves of a plant called Mitragyna speciosa or Kratom. In addition, the psychoactive agent Salvinorin A that induces psychedelic effects is found in the Salvia divinorum plant.

Opioids present in the body or endogenous opioids

Semisynthetic opioidsExamples of endogenous opioids include enkephalins, dynorphins, endorphins and endomorphins.

These are synthesized from the natural opioids and include:

• Hydrocodone
• Oxycodone
• Hydromorphone
• Oxymorphone
• Desomorphine
• Heroin or diacetylmorphine
• Nicomorphine
• Benzylmorphine
• Ethylmorphine
• Dipropanoylmorphine
• Buprenorphine

Synthetic opioids

These opioids are synthesized chemically in the laboratory and are agents commonly used in pain relief, treating drug dependence and anesthesia. Examples include:

• Pethidine
• Tramadol
• Methadone
• Fentanyl
• Dextropropoxyphene

Opioid-like agents

Examples of opioid-like agents include tramadol and tapentadol, which are chemically dissimilar to opioids but do have some affinity for the μ-opioid Receptor. These agents also act on the noradrenergic and serotonergic systems to relieve pain.

Opioid classes

According to the Drug Enforcement Agency, there are 4 chemical classes of opioids and these include:

• Phenanthrenes or typical opioids that contain a 6-hydroxyl group. This group includes morphine, codeine, hydromorphone, hydrocodone, oxymorphone, levorphanol, nalbuphine, buprenorphine and oxycodone.
• Benzomorphans such as pentazocine.
• Phenylpiperidines which includes fentanyl, alfentanil and meperidine.
• Diphenylheptanes including methadone and propoxyphene.