opioid
Meaning of opioid: These drugs do not remove the source of pain; they change how the nervous system registers it, and the other effects follow from that.
Definition of opioid
An opioid is any substance that acts on the body's opioid receptors, which sit throughout the brain, spinal cord and gut. The class covers plant-derived opiates such as morphine and codeine, semisynthetic drugs made from them, fully synthetic ones such as fentanyl and methadone, and the body's own endorphins. Medically they are used mainly for moderate to severe pain.
What are the different kinds?
| Group | Origin | Examples |
|---|---|---|
| Endogenous | Made by the body | Endorphins, enkephalins, dynorphins |
| Opiates | Extracted from the opium poppy | Morphine, codeine |
| Semisynthetic | Chemically modified from an opiate | Oxycodone, hydrocodone, buprenorphine, heroin |
| Synthetic | Built without poppy-derived material | Fentanyl, methadone, tramadol |
Opiate refers only to the poppy-derived members, so every opiate is an opioid but not the reverse. A rapid-onset opioid is one formulated to take effect within minutes rather than over hours.
How do they work, and what else do they do?
Opioid receptors sit on nerve cells at several points along the pain pathway, in the spinal cord where signals arrive, in the brainstem where descending control originates, and in regions that give pain its emotional weight. A drug binding there dampens transmission and, just as importantly, changes how unpleasant the sensation feels. Receptors elsewhere in the nervous system and in the gut account for the rest: drowsiness, euphoria, nausea, itching, pinpoint pupils, and constipation that persists for as long as the drug is taken. Slowed breathing is the effect that makes an overdose dangerous, because the drive to breathe is suppressed before consciousness is fully lost.
What happens with continued use?
Two things develop that are often confused. Tolerance means a given dose produces less effect over time. Physical dependence means the body has adjusted to the drug's presence and produces withdrawal symptoms when it is stopped or reduced. Both are predictable physiological responses and both occur in people using opioids exactly as directed. Addiction is a separate condition defined by compulsive use and continued use despite harm, and it is neither the same as dependence nor an inevitable result of it. Confusing the three has caused a great deal of misunderstanding in both directions.
Used in a sentence
An opioid was prescribed for short-term management of severe postoperative pain.
Good to know
Narcotic was once used interchangeably with opioid but is now applied inconsistently, sometimes in a legal sense covering a much broader range of controlled substances, so opioid remains the precise term for this drug class.
Word origin
Where “opioid” comes from
Formed from opium, from Greek opion, meaning poppy juice, and -oid, from Greek -oeides, meaning resembling.