What it is used for

Helping prevent relapse after stopping opioids
Helping prevent relapse in alcohol dependence

Read our guides:

Off-label uses

Doctors sometimes prescribe a medicine for a condition it is not officially licensed for. This is called off-label use. It is legal and common when there is good evidence it helps, and your doctor should explain why they are suggesting it.

Low doses for some long-term pain conditions such as fibromyalgia (limited evidence, specialist only)
Itching caused by liver disease

How it works

Naltrexone blocks opioid receptors in the brain. Opioids taken during treatment have little or no effect, and the rewarding effect of alcohol is reduced, which helps lower cravings.

Side effects

Like all medicines, Naltrexone can cause side effects, although not everyone gets them. Many are mild and ease after the first few weeks.

Common side effects

feeling sick
headache
trouble sleeping
feeling anxious or restless
stomach pain
joint and muscle pain

Tell your doctor or pharmacist if these bother you or do not go away.

Serious side effects

These are rare. Call 111 or contact your doctor straight away if you get:

yellowing of the skin or eyes, dark pee or pale poo
low mood or thoughts of harming yourself

Call 999 if you have signs of a serious allergic reaction, such as swelling of your lips, mouth, throat or tongue, or trouble breathing.

You can report any side effect to the Yellow Card scheme, run by the medicines regulator.

Stopping and withdrawal

Important safety information

You must be completely off opioids for 7 to 10 days before starting, or it will cause sudden, severe withdrawal.
Carry a card saying you take naltrexone, as normal opioid painkillers will not work.
Do not try to overcome the block by taking large amounts of opioids. This can be fatal.

Questions about your medicine?

A pharmacist can answer questions about your medicines for free, without an appointment. You can also ask your GP for a medication review. Check if you can get free prescriptions.