Who should avoid naltrexone is the first question worth asking, and it deserves a better answer than a bare list of conditions. Naltrexone helps a great many people. However, it also carries a small number of absolute stops, and one of them can cause a medical emergency within minutes of a single tablet.
So this guide starts with what the drug actually does, then walks through those stops in plain English. It covers the medicines that clash, the opioid-free wait, the liver thresholds that matter, and the situations that call for caution rather than avoidance. Knowing who should avoid naltrexone before your appointment means you arrive able to flag the right things early.
First, one thing to be clear about. This article helps you prepare for a clinical assessment. It does not replace one.
Please read this first if you get shakes, sweats or bad anxiety in the morning, or you drink to steady yourself, do not stop or cut down on your own. Sudden cuts in heavy drinking can cause seizures. Speak to your GP or alcohol service first.
Five Key Takeaways
- Opioids are the absolute stop. Take this drug with opioids in your system, and you can suffer a sudden, severe withdrawal. This starts within minutes and can threaten life.
- The UK licence bans it in severe kidney disease. Many articles call this a caution. In Britain, it sits in the contraindications list alongside severe liver problems.
- Breastfeeding advice differs here. The UK leaflet advises against breastfeeding while you take it. American sources often say otherwise.
- Stable liver disease is not automatically a stop. Acute hepatitis and liver failure are. Compensated disease becomes a topic for monitoring instead.
- Some very ordinary purchases count as opioids. Co-codamol, Nurofen Plus, co-dydramol, codeine linctus and loperamide all matter here.
What Naltrexone Is Used For, and Who Should Avoid It
Before the stops, some context. Naltrexone is not a new drug, and it is not a sedative or a tranquilliser. It blocks opioid receptors in the brain, which is a simple action with several uses.
The licensed use in the UK. In Britain, naltrexone holds a licence for two things. First, it supports people recovering from opioid addiction, by blocking the effect of opioids entirely. Second, it forms part of a wider programme for alcohol dependence, where it cuts craving and lowers the risk of a full relapse.
That second use is the one most readers arrive here for. Taken daily at 50 mg, alongside psychological support, it takes some of the pull out of drinking.
One point deserves emphasis. The licence describes naltrexone as part of a programme, not as a treatment on its own. A prescription without support behind it is only half a plan.
The Sinclair Method
Interest in the Sinclair Method has grown sharply, and it is probably why you are reading this.
The approach uses the same drug in a different rhythm. Instead of a daily tablet, you take one an hour or two before you plan to drink. The theory is that pairing alcohol with a blocked reward, session after session, slowly weakens the habit. Supporters call this pharmacological extinction.
The idea is plausible, and some people report real change. However, two things are worth knowing before you go further. No UK guideline recommends this timing, so using naltrexone this way is off-label. And the success rates you see quoted, usually around 78%, trace back to the method’s founder and the services that sell it rather than to independent trials.
There is also a licensed alternative that rarely gets a mention. Nalmefene is taken on days you expect to drink, and NICE recommends it for people cutting down from a high level. Most UK prescribers will raise that first.
Our Sinclair Method guide covers the evidence and the comparison in full.
Low dose naltrexone
Off-label and low-dose uses. You may also have seen naltrexone discussed at much smaller doses, usually between 1 mg and 5 mg, for conditions such as fibromyalgia, chronic pain or long COVID. That is a separate world, generally called low-dose naltrexone, and it is entirely off-label.
Importantly, the safety rules below still apply at any dose. The opioid block is the opioid block, so anyone taking opioids should avoid naltrexone whether the tablet is 50 mg or 3 mg.
Pharmacist’s tip whichever use brings you here, the screening questions are the same. That is why this article covers them once rather than three times.
Who Should Avoid Naltrexone Completely
The UK leaflet lists a clear set of absolute stops. These are not judgement calls. If one applies to you, a prescriber will not start this medicine.
- Current opioid use, or opioid dependence. More on this below, because it is the big one.
- Anyone taking opioid painkillers, or any medicine containing an opioid.
- Anyone taking methadone.
- A positive urine test for opioids.
- A positive naloxone challenge test.
- Acute hepatitis, or liver failure.
- Severe or acute liver impairment.
- Severe kidney trouble.
- Known allergy to naltrexone or to anything else in the tablet.
- Rare inherited sugar problems. The licensed tablets contain lactose, so anyone with a rare inherited sugar problem should not take them. Your GP will have told you if this applies.
That last one surprises people because hardly any articles mention it. However, for those with this condition, it is useful to bear in mind that Courier Pharmacy uses compounded medicines which are suitable for vegetarians and lactose-free.
Pharmacist’s tip bring a full medicines list, including anything you buy yourself. Half the items on the stop list are things patients do not think of as medicines at all.
Opioids: Why They Top the Avoid List
Here is why opioids sit at the top of every list of absolute stops.
It blocks opioid receptors fast and fully. If your body has got used to opioids, that block does not ease you off gently. It strips the opioid effect away all at once, which sets off what doctors call precipitated withdrawal.
In fact, they can start within minutes of the first tablet. They include violent sickness, stomach cramps, sweating, agitation, muscle pain and chills. They can run for 24 to 48 hours or longer. That is an emergency, not a rough patch.
Meanwhile, cutting the dose does not help. Any real dose will do it if opioids are still on board.
How long you should avoid naltrexone after opioids
In short, the waiting time depends on what you were taking.
Short-acting opioids such as heroin, codeine and oxycodone clear faster. The UK leaflet suggests roughly five to seven days for heroin. Many services apply a more cautious 7 to 10 days, and that extra margin is sensible rather than fussy.
Long-acting opioids need longer. For methadone, the UK licence specifies at least 10 days. Buprenorphine is treated similarly, and some services extend to 14 days.
Opioid-free means exactly that. Reduced use does not count, nor does occasional use, nor does “only at weekends”.
How your prescriber confirms it. First, a urine drug screen is standard, and a positive result means waiting rather than starting. Where doubt remains after the history and the screen, a naloxone challenge test may follow. Naloxone is given in a controlled setting, and any withdrawal signs mean treatment must not begin.*
*urine tests not required for LDN and the Sinclair Method unless there is a known opioid drug problem.
Anyone using opioids should avoid naltrexone until they have been completely opioid-free. UK guidance suggests around five to seven days for heroin and at least 10 days for methadone, confirmed by urine screening.
Liver Disease: Who Should Avoid Naltrexone, and Who Should Not
Because your liver breaks this drug down, liver health shapes the decision.
First, acute hepatitis, liver failure and severe or acute liver impairment are absolute stops. Stable, well-run liver disease is a different matter, and often workable with checks.
What blood tests say about who should avoid naltrexone
For instance, ALT and AST are enzymes that rise when liver cells become inflamed or damaged. Labs compare your result against the upper limit of normal, or ULN.
Broadly, prescribers read the picture like this. Results up to around three times the ULN often allow treatment with closer monitoring. Above three times, your prescriber should investigate first, and the UK leaflet flags that level for special care. Far above it, particularly alongside jaundice or abdominal pain, naltrexone should not start at all.
Still, two pieces of context help. Liver harm is rare at the 50 mg dose used for alcohol, and the worrying historical results came from doses several times higher. Raised enzymes during treatment also tend to fall back once the medicine stops.
Checks afterwards. Then your prescriber should test liver function before you start and again during treatment. Every six months is common. Closer checks apply if the first test was abnormal, or if you already have liver disease.
Contact your GP immediately if you notice yellowing of the skin or eyes, dark urine, pale stools, ongoing sickness, or pain in the upper right of your abdomen.
Kidneys: A UK Difference Worth Knowing
This point deserves its own section, because plenty of articles get it wrong.
Second, the drug leaves your body mainly through the kidneys. American sources often treat reduced kidney function as a caution. The UK licence goes further. It lists severe kidney trouble as a hard stop, in the same list as severe liver disease.
That said, mild or moderate impairment is not an automatic stop. It does mean closer watching, and your prescriber may adjust the dose.
So if you have any kidney condition, say so early. Recent blood tests will speed the conversation considerably.
Who Should Avoid Naltrexone in Pregnancy and Breastfeeding
Pregnancy is not listed as an absolute contraindication, yet doctors do not recommend it as a first choice either. Human safety data remain thin, and UK guidance does not back routine use of relapse-prevention medicines in pregnancy. Women who conceive while settled on it are usually advised to stop, though a clinician decides case by case.
Therefore, weigh this carefully rather than treating it as simple. Alcohol harms a developing baby, so the risk of relapse has to sit on the scales alongside the uncertainty about the medicine. That balance needs a doctor, not a search engine.
Breastfeeding is where UK advice splits from what you read elsewhere. American sources often call it probably safe while breastfeeding. The UK leaflet says plainly that you should not breastfeed during treatment. Besides, nobody knows whether the drug passes into human milk.
If you are breastfeeding and considering treatment, ask your prescriber directly which position they follow and why.
Under-18s fall outside the licence. Doctors do not use it below 18 for this purpose, because we lack safety and efficacy data. Any decision needs a specialist rather than a routine route.
Medicines That Clash With Naltrexone
Things you can buy over the counter
For example, many UK pharmacy products contain opioids, and shoppers rarely think of them that way.
- Co-codamol, which combines paracetamol and codeine
- Nurofen Plus, which combines ibuprofen and codeine
- Co-dydramol, which combines paracetamol and dihydrocodeine
- Codeine linctus and similar cough remedies
- Loperamide-based anti-diarrhoea products
Yet this drug blocks all of them. In anyone dependent on opioids, taking one can trigger withdrawal.
Prescribed painkillers.
Starting treatment and later needing opioid pain relief creates a real problem. Because of the blockade, normal doses will not work. Pushing the dose higher to overcome it risks dangerous breathing problems.
So if you have surgery booked, or you expect to need opioid pain relief soon, raise the timing before you start rather than afterwards.
Other medicines.
In addition, disulfiram, sometimes used for alcohol dependence, interacts with it moderately. Both place some load on the liver, and using them together increases it.
Use sedating medicines with care alongside it. That group covers benzodiazepines, sleeping tablets, sedating antidepressants and sedating antihistamines. Thioridazine has been linked with drowsiness and lethargy in combination. Certain blood pressure medicines are not recommended together either.
Who Should Avoid Naltrexone Versus Who Needs Monitoring
However, blurring these two groups is the most common mistake in articles on this topic. They are quite different.
| Situation | Where it sits |
| Current opioid use or dependence | Absolute stop |
| Acute hepatitis or liver failure | Absolute stop |
| Severe kidney trouble | Absolute stop in the UK |
| Allergy to naltrexone or its ingredients | Absolute stop |
| Rare inherited sugar problem | Absolute stop* |
| Stable cirrhosis | Possible, with checks and specialist input |
| Mild or moderate kidney trouble | Possible, with close watching |
| Mildly raised liver enzymes | Usually possible, with closer checks |
| Taking disulfiram | Possible, with the liver load considered |
| Pregnancy | Not routine, decided case by case |
| Breastfeeding | Not recommended in the UK |
| Under 18 | Outside the licence, it needs a specialist |
*Compounded preparations supplied by Courier Pharmacy are vegetarian and lactose-free, and so if used, are not a hard stop
Still, landing in the second half of that table is not a no. It just shifts the talk from ‘whether’ to ‘how’.
Compounding at Courier
When the standard option isn’t the right fit, we can make one to order
Courier is a compounding pharmacy. Where a prescriber decides it’s appropriate for you, we can prepare bespoke, made-to-order preparations — tailored to the individual, under full clinical governance. It’s the same principle that runs through everything we do.
Deciding Who Should Avoid Naltrexone: Your Assessment
In practice, a proper assessment should ask about all of the following. If yours skips several, that is worth questioning.
- Every medicine you take, including anything bought over the counter
- Your opioid history, and the date you last used any
- Liver and kidney function, with recent blood results
- Your drinking pattern, and whether you get physical withdrawal symptoms
- Pregnancy, planned pregnancy, or breastfeeding
- Mental health history, including any thoughts of self-harm
- Allergies, including reactions to fillers and coatings
- Upcoming surgery or anticipated need for pain relief
At Courier Pharmacy, a UK-registered prescriber reviews every enquiry against exactly this list. No algorithm makes the decision, and no prescription follows without that review.
Our alcohol addiction page explains what we can and cannot offer. If you want to understand the targeted dosing approach first, our Sinclair Method guide covers the evidence and the licensed alternative.
If You Should Avoid Naltrexone, What Next?
Of course, finding that you fall into a stop category is frustrating. It is not a dead end.
Sometimes the barrier is temporary. An opioid-free window passes. Liver enzymes settle. A course of painkillers finishes. Your prescriber can tell you what would need to change and roughly when to ask again.
Instead, another medicine may fit better. Nalmefene is licensed in the UK to cut heavy drinking, and acamprosate suits people aiming to stop. Both have different safety profiles, so one stop here does not rule them out.
And sometimes the answer is not a tablet at all. NHS alcohol services offer counselling, structured support and medical supervision free of charge, and self-referral is usually possible. For someone with physical dependence, that route is the safer one anyway.
Summary
Understanding who should avoid naltrexone comes down to a short list of absolute stops and a longer list of situations needing care. The absolute stops are opioids in any form, acute liver disease, severe kidney trouble, allergy, and rare inherited sugar problems (does not apply to compounded lactose-free capsules).
Two UK-specific points are worth carrying into your appointment. Severe kidney trouble is a hard stop here, not a caution. And the UK leaflet advises against breastfeeding during treatment, which contradicts much of what you will read online.
Otherwise, everything else moves the talk towards checks rather than avoidance. That covers stable liver disease, mild kidney trouble and slightly raised enzymes.
If you worry about your drinking, your GP or local alcohol service is a good place to start. Courier Pharmacy offers clinician-led appointments for people who want a structured private route with proper follow-up.
FAQs
Who should avoid naltrexone completely?
Anyone using opioids or hooked on them, anyone with acute hepatitis or liver failure, anyone with severe liver or kidney trouble, anyone allergic to it, and anyone with a rare inherited sugar problem.
How long must I be opioid-free before starting?
Around five to seven days after heroin, and at least 10 days after methadone. Many services apply longer margins. A urine screen confirms it.
Can I take naltrexone with liver disease?
Not with acute hepatitis, liver failure, or severe impairment. Stable disease may allow treatment with checks and specialist input.
Does kidney disease mean I should avoid naltrexone?
Severe kidney trouble is a hard stop in the UK. Mild or moderate impairment calls for close watching, not avoidance.
Can I take it while pregnant or breastfeeding?
Naltrexone is not routinely recommended in pregnancy, and decisions happen case by case. The UK leaflet advises against breastfeeding while you take it.
Which over-the-counter medicines clash with naltrexone?
Co-codamol, Nurofen Plus, co-dydramol, codeine linctus and loperamide products all contain or act on opioids. Check with a pharmacist before buying anything.
What if I need surgery while taking naltrexone?
Tell the surgical team you take it. Opioid pain relief will not work normally, so they need to plan around that in advance.
Are there alternatives if I should avoid naltrexone?
Yes. Nalmefene is licensed for reducing high-level drinking, and acamprosate supports abstinence. NHS alcohol services also provide counselling and supervision free of charge.
This article is for information only. It does not replace a clinical assessment. This is a prescription-only medicine. Only a clinician experienced in alcohol treatment should start it.
References
- British National Formulary (BNF) (n.d.) Naltrexone hydrochloride. Available at: https://bnf.nice.org.uk/drugs/naltrexone-hydrochloride/ (Accessed: 2 August 2026).
- Department of Health and Social Care (2025) Clinical guidelines for alcohol treatment. GOV.UK. Available at: https://www.gov.uk/guidance/clinical-guidelines-for-alcohol-treatment (Accessed: 1 August 2026).
- National Institute for Health and Care Excellence (2011) Alcohol-use disorders: diagnosis, assessment and management of harmful drinking (high-risk drinking) and alcohol dependence. NICE guideline CG115. Available at: https://www.nice.org.uk/guidance/cg115 (Accessed: 1 August 2026).
- National Institute for Health and Care Excellence (2014) Nalmefene for reducing alcohol consumption in people with alcohol dependence. NICE technology appraisal guidance TA325. Available at: https://www.nice.org.uk/guidance/ta325(Accessed: 1 August 2026).
- Sinclair Method. What is the Sinclair Method? Available at: https://www.sinclairmethod.org/what-is-the-sinclair-method-2/
- Courier Pharmacy (2026) The Sinclair Method for alcohol use disorder: how it works. Available at: https://courierpharmacy.co.uk/the-sinclair-method-for-alcohol-use-disorder-how-it-works/ (Accessed: 1 August 2026).
- Harvard Health Publishing. Can you retrain your brain to stop excessive drinking? Available at: https://www.health.harvard.edu/medications-and-treatments/can-you-retrain-your-brain-to-stop-excessive-drinking
- Courier Pharmacy. The Sinclair Method for alcohol dependence, UK guide. Available at: https://courierpharmacy.co.uk/the-sinclair-method-blocking-endorphin-driven-reward/
- Courier Pharmacy (2026) Can you drink while on the Sinclair Method? a UK guide. Available at: https://courierpharmacy.co.uk/can-you-drink-while-on-the-sinclair-method-a-uk-guide/ (Accessed: 2 August 2026).
