naltrexone
Meaning of naltrexone: Blocking rather than replacing sets it apart from methadone and buprenorphine, and it is why timing after withdrawal matters so much.
Definition of naltrexone
Naltrexone is an opioid antagonist, a medicine that occupies opioid receptors without switching them on and so blocks any opioid that arrives. It is used in opioid use disorder, once withdrawal is complete, and in alcohol use disorder, where it appears to dull the reward of drinking. It comes as a daily tablet and as a monthly injection.
How is it different from naloxone?
| Naltrexone | Naloxone | |
|---|---|---|
| Purpose | Ongoing treatment that blocks the effect of opioids | Emergency reversal of an overdose |
| How it is given | Tablet daily, or an injection lasting about a month | Nasal spray or injection, acting within minutes |
| Duration | Long | Short, often shorter than the opioid it reverses |
| Setting | Planned, after withdrawal is complete | Unplanned, at the point of collapse |
The names are close enough to be confused, and both act as an antagonist at the same receptors, but they belong to entirely different situations.
Why must opioids be out of the system first?
An antagonist displaces whatever is sitting on the receptor. In someone physically dependent on opioids, that displacement triggers withdrawal all at once rather than over hours, a state called precipitated withdrawal, with severe agitation, vomiting, diarrhea, cramps and sweating. It is not usually dangerous in itself but it is intensely unpleasant and hard to stop once started. For that reason a defined opioid-free interval is required before starting, and its length depends on which opioid was used. The block also works in the other direction: while the drug is active, opioid painkillers will not work normally, which matters if an injury or an operation occurs.
How is it used in alcohol use disorder?
Drinking triggers release of the body's own opioid-like chemicals, which is part of what makes it rewarding. Blocking those receptors appears to reduce that reward and, in trials, reduces heavy drinking days rather than guaranteeing abstinence. It is one of several medicines used for what was formerly called alcohol dependence and is now more often termed alcohol use disorder. Unlike disulfiram it produces no reaction if a person drinks; it simply makes drinking less rewarding, and blunting the euphoria is the shared mechanism in both of its main uses. Nausea, headache, tiredness and dizziness are the usual effects, and liver tests are monitored during treatment.
Also known as
Used in a sentence
Naltrexone was included in the patient's ongoing treatment plan for opioid use disorder.
Good to know
Naltrexone must be distinguished from naloxone, a related opioid antagonist used to reverse acute opioid overdose, since the two share a mechanism but are used in very different clinical situations.