The term opioid refers to a class of natural, semi-synthetic, and synthetic compounds that bind to and activate opioid receptors in the brain, spinal cord, and other parts of the body. These substances work by blocking pain signals and producing feelings of relaxation or euphoria.
Opioids include:
Natural opium alkaloids – such as morphine and codeine, derived from the opium poppy (Papaver somniferum)
Semi-synthetic opioids – such as heroin, oxycodone, and buprenorphine
Fully synthetic opioids – such as methadone, fentanyl, and pethidine (meperidine)
Endogenous opioids – naturally occurring neuropeptides in the brain, such as endorphins and enkephalins, which modulate pain and mood
Therapeutically, opioids are used to manage moderate to severe pain and support opioid use disorder treatment (e.g., methadone maintenance). However, chronic use can lead to tolerance, physical dependence, and addiction.
Overdose from opioids can cause respiratory depression, stupor, or death. Withdrawal symptoms may include cravings, anxiety, insomnia, muscle aches, and gastrointestinal distress, varying in duration depending on the specific opioid used.
Sources: UPenn; ProjectKnow; Gosnold; Recovery Research Institute; HRB