Naltrexone Side Effects: What's Common, and What's Rare?
By Rethink Drink.
Yes, naltrexone can cause side effects.
The ones the UK patient leaflet lists as very common (more than 1 in 10 people) are nausea, being sick, stomach pain, headache, trouble sleeping, feeling anxious, nervous or restless, joint and muscle pain, and feeling weak.
The serious ones are much rarer. But you need to know them... and two warnings matter more than any side effect: your liver, and opioid medicines, including some everyday painkillers.
You might be reading this before you start.
Or you might already be taking it, feeling rough, and wondering whether it's the tablet or something else.
On calls, people often ask us some version of "will it make me feel ill?" Here's what the official UK leaflet says.
Whether naltrexone is right for you is a decision for a prescriber who knows your health.
In short
The common ones: nausea, headache, trouble sleeping, anxiety or restlessness, stomach pain, being sick, joint and muscle aches, feeling weak. The leaflet lists all of these as very common.
The serious ones are rare or uncommon: low mood, depression, hallucinations and confusion are uncommon. Suicidal thoughts are rare. If you notice any of them, contact your doctor or pharmacist straight away.
Your liver: liver problems, including hepatitis, are listed as uncommon. Your liver is checked with a blood test before you start, and during treatment.
Opioids: naltrexone blocks opioid medicines. That includes codeine, tramadol and some cough, cold and diarrhoea medicines. Never try to override the block by taking more.
Don't stop or change it on your own. Speak to your prescriber or pharmacist first.
Check first: if your body depends on alcohol, stopping or cutting down too fast can be dangerous. Speak to your GP (General Practitioner) or local alcohol service before you change anything...
...Our free units calculator and AUDIT-C check give you a starting picture in a couple of minutes. They can't tell you whether your body depends on alcohol; a doctor can.
What are the side effects of naltrexone?
Every medicine sold in the UK comes with a patient leaflet. It lists the known side effects, grouped by how often they happen.
The figures below come from the patient leaflet for Adepend, a naltrexone tablet licensed in the UK for alcohol dependence, and its product information for doctors. Other brands of naltrexone carry very similar lists. The leaflet in your own pack is the one to read.
How often | What the leaflet means | Side effects listed |
|---|---|---|
Very common | More than 1 in 10 people | Anxiety, trouble sleeping, headache, restlessness, nervousness, stomach pain, nausea, being sick, joint and muscle pain, feeling weak |
Common | 1 to 10 in every 100 people | Reduced appetite, palpitations, a faster heartbeat, chest pain, changes in sex drive, erection or ejaculation problems, thirst, dizziness, watery eyes, diarrhoea, constipation, rash, feeling more energetic, irritability, more sweating, changes in mood |
Uncommon | 1 to 10 in every 1,000 people | A long list, including low mood and depression, hallucinations, confusion, nightmares, shaking, drowsiness, blurred or changed vision, liver problems including hepatitis, hair loss, itching, acne, weight changes and fever |
Rare | 1 to 10 in every 10,000 people | Suicidal thoughts and suicide attempts, a low platelet count (which can affect blood clotting) |
Very rare | Fewer than 1 in 10,000 people | Breakdown of muscle tissue |
A table can't tell you what you'll feel. It's a starting point for a conversation with your prescriber or pharmacist.
Read that table the right way round...
A side effect being "very common" means more than 1 in 10 people taking it reported it. It doesn't mean you'll get it.
Is it the tablet, or is it cutting down?
This is one of the most useful questions to ask. And it isn't always easy to answer.
Some of what people put down to naltrexone can also come from changing how much you drink.
Two examples.
Sleep. Passing out isn't sleep. When you drink less, the first nights can feel rough, and you can wake up shattered... It's easy to blame that tiredness on the tablet.
Feeling flat. Life can feel flat while you're cutting down, as well as on the tablet. Your brain is adjusting to less alcohol. That's a big change, whatever the reason for it. More on that here: Does naltrexone block all pleasure?
But here's the important part...
Anxiety, nausea and trouble sleeping can also be signs of alcohol withdrawal, if your body depends on alcohol and you've cut down quickly. The NHS lists all three as withdrawal symptoms.
So don't guess. If something feels wrong, tell your prescriber or pharmacist what you're feeling, and how your drinking has changed. They can help you work out which is which.
What are the serious side effects of naltrexone?
These are the ones not to sit on.
Low mood, depression and suicidal thoughts. The leaflet lists depression as uncommon, and suicidal thoughts and suicide attempts as rare. An NHS hospital's naltrexone leaflet says that if you notice low mood, suicidal feelings or hallucinations, contact your doctor or pharmacist immediately.
The doctors' product information adds something honest too. People who drink heavily or use drugs already have a higher risk of suicide, and naltrexone doesn't reduce that risk. So if your mood drops, it matters, whatever is causing it.
Hallucinations and confusion. Listed as uncommon. Same advice: contact your doctor or pharmacist straight away.
Liver problems. More on these below.
What does naltrexone do to your liver?
Naltrexone is processed by the liver. So the liver matters, before you start and while you take it.
What the UK product information says:
It's not suitable for people with acute hepatitis, liver failure, or severe liver problems.
Your liver is checked first. Liver function blood tests are done before you start, and during treatment.
Liver problems are uncommon side effects. The list includes liver disorders, raised bilirubin and hepatitis.
Liver test results can rise during treatment. The product information says they usually go back to where they were within several weeks of stopping.
It can affect blood test results. The leaflet says to tell staff you take it before any blood test.
What to watch for...
If your skin or the whites of your eyes turn yellow, that's jaundice. The NHS says to ask for an urgent GP appointment or get help from NHS 111. Tell them you take naltrexone.
Why does naltrexone matter if you take opioid painkillers?
This is the warning that matters most, and it isn't really a side effect. It's how the medicine works.
Naltrexone blocks the brain's opioid receptors. That's the same place opioid medicines work.
So, per the leaflet and product information:
Opioid painkillers may not work properly. That includes codeine and tramadol.
Some everyday products contain opioids. Some cough, cold and diarrhoea medicines, and some painkillers you can buy in a pharmacy. Ask your pharmacist before you buy anything.
Don't take naltrexone if you're dependent on opioids. It can bring on sudden, severe withdrawal, which can be life-threatening.
Never try to override the block by taking more of an opioid. The leaflet warns that when naltrexone wears off, you could overdose, and that can be fatal.
After you stop naltrexone, you may be more sensitive to opioids than before.
In an emergency, pain relief may need to be handled differently, with close monitoring. Tell every doctor who treats you that you take naltrexone.
We've covered all of this, medicine by medicine, here: Does naltrexone interact with other medications?
Who shouldn't take naltrexone?
Your prescriber checks this. But it helps to know what they're looking for.
Per the UK product information, naltrexone isn't suitable if you:
Have acute hepatitis, liver failure or severe liver problems.
Have severe kidney problems.
Take opioid painkillers, other opioid medicines, or methadone.
Are dependent on opioids, or have opioids in your system (your prescriber may test for this).
Are allergic to naltrexone or anything else in the tablet.
And speak to your doctor first if you're pregnant, breastfeeding, or planning a pregnancy.
Can you drive on naltrexone?
The leaflet says it can affect the mental and physical abilities you need for things like driving or using machines. The Adepend leaflet goes further: it says driving vehicles should be avoided.
Check the advice in your own pack. Don't drive if you feel drowsy, dizzy or not yourself, and ask your pharmacist if you're unsure.
What should you do if you get side effects?
Tell your prescriber or pharmacist. Any side effect that becomes serious, or isn't in the leaflet, is worth reporting to them.
Don't stop or change the medicine on your own. The leaflet says not to stop treatment without speaking to your doctor first.
Get help fast for the serious ones. Low mood, suicidal thoughts, hallucinations, confusion or yellowing skin or eyes.
You can report it yourself. The UK's Yellow Card scheme, run by the medicines regulator, takes reports from patients as well as doctors.
Does it matter how naltrexone is used?
The side effects are listed for the medicine. Not for the method.
But naltrexone is used in two completely different ways, so it's worth being clear which one you're on.
Same medicine. Two methods. Two goals.
In its usual NHS use, it's taken once you've stopped drinking, to help you stay stopped. That's its UK licence.
The Sinclair Method uses it before drinking, at a time your prescriber sets, while you're still drinking, to drink less over time. That use is off-label in the UK. It's explained here: What is The Sinclair Method?
Either way, your prescriber decides how and when you take it. And either way, the same leaflet, and the same warnings about your liver and opioids, apply.
Our full explainer on the medicine: Naltrexone for alcohol in the UK.
If you tried it before and didn't like how it felt, that's worth a proper look too: Naltrexone didn't work for me. Why?
Common questions
Does naltrexone make you feel sick?
It can. Nausea is listed as very common, which means more than 1 in 10 people reported it. If it's bothering you, speak to your prescriber or pharmacist rather than stopping on your own.
Does naltrexone cause weight gain or weight loss?
Both are listed in the leaflet, as uncommon. Reduced appetite is listed as common.
Is naltrexone addictive?
The Adepend leaflet says it doesn't cause dependency.
Does naltrexone affect sex drive?
Changes in sex drive, and erection or ejaculation problems, are listed as common.
Can naltrexone damage your liver?
Liver problems, including hepatitis, are listed as uncommon. That's why your liver is checked before and during treatment, and why it isn't prescribed to people with serious liver disease.
Can I take paracetamol or ibuprofen on naltrexone?
Neither is an opioid. But some combination painkillers contain codeine, which is. Check the label, and ask your pharmacist before you buy.
If you'd like support from us
Rethink Drink is a UK coaching service built around The Sinclair Method. Our programmes include a consultation with an independent prescriber, who decides whether treatment is suitable for you. Any prescription is dispensed by an independent partner pharmacy. Our coaches work with you, week by week, on everything around it.
And whatever happens, you can talk to someone today. Drinkline, the national alcohol helpline, is free and confidential: 0300 123 1110.
Please look after yourself
This page is here to help you understand your options. It isn't medical advice, and it can't replace a conversation with a doctor who can ask qualifying questions.
Before you change how much you drink or start any medication, speak to your GP or a prescriber.
If you're struggling with low mood or thoughts of harming yourself, Samaritans are free, any time, on 116 123.
We really hope this post helps. If you have any questions, you can contact us here.
The Rethink Drink team
Sources
AOP Orphan. Adepend film-coated tablets (naltrexone hydrochloride): Patient Information Leaflet (emc; leaflet last approved December 2021; product now listed as discontinued). https://www.medicines.org.uk/emc/files/pil.3559.pdf
AOP Orphan. Adepend film-coated tablets (naltrexone hydrochloride): Summary of Product Characteristics (emc; product now listed as discontinued). https://www.medicines.org.uk/emc/product/3559/smpc
Royal Free London NHS Foundation Trust. Naltrexone: patient information leaflet (approved September 2025). https://www.royalfree.nhs.uk/patients-and-visitors/patient-information-leaflets/naltrexone
NHS. Alcohol use disorder (page last reviewed 24 April 2026). https://www.nhs.uk/conditions/alcohol-use-disorder/
NHS. Jaundice (page last reviewed 22 January 2024). https://www.nhs.uk/conditions/jaundice/
Department of Health and Social Care. UK clinical guidelines for alcohol treatment, chapter 10: pharmacological interventions. https://www.gov.uk/guidance/clinical-guidelines-for-alcohol-treatment/10-pharmacological-interventions
NHS. About codeine (page last reviewed 9 June 2026). https://www.nhs.uk/medicines/codeine/about-codeine
NHS. About tramadol (page last reviewed 4 February 2026). https://www.nhs.uk/medicines/tramadol/about-tramadol/
Medicines and Healthcare products Regulatory Agency. Yellow Card scheme (as signposted in the leaflet above). https://yellowcard.mhra.gov.uk/
