Common side effects of naltrexone (and how to manage them)

Naltrexone is a well-established medicine, prescribed since the 1990s, and most people tolerate it well. The side effects that do happen are usually mild and limited to the first week or two.

This is the one most people notice, a slightly queasy feeling for an hour or two after the tablet. It usually settles within one to two weeks as your body adjusts.

What helps:

• Take the tablet with food rather than on an empty stomach

• Build up gradually, from a quarter tablet to a half, three-quarters, then full over two to three weeks, which softens side effects a lot

• Stay well hydrated, especially in the first few days

• If nausea is still there past two weeks, message us; we can adjust the schedule or consider nalmefene

Some people get mild headaches in the first week, usually eased by paracetamol. If they are persistent or severe, get in touch.

A subtle dip in energy is sometimes reported in the first week, a slightly flatter feeling as the brain adjusts to having its opioid receptors blocked. It passes.

Rarely, people report a brief low mood in the first week or two, usually mild and self-limiting. If you have a history of depression we will have flagged it at your assessment and we will check in closely. If you notice persistent low mood, or any thoughts of self-harm, contact us straight away.

Naltrexone is processed by the liver and, very rarely, causes a temporary rise in liver enzymes. We keep an eye on this with a simple blood test at baseline, then one to three months in, and occasionally after that. If the numbers rise meaningfully we would move you to nalmefene, which needs no routine liver monitoring.

Naltrexone blocks the receptors opioids work on, so two things follow: opioid painkillers like codeine, tramadol or morphine will not work while you take it, and if you are dependent on opioids it can bring on withdrawal. It is less a toxic danger than the two cancelling each other out, but it is why we screen carefully for opioid use. If you have taken any opioid in the days before starting, tell us. Nalmefene works the same way, so it is no way round this.

Worth being clear, because it is a safety point, not a side effect: naltrexone does nothing to the alcohol itself. You still get drunk, still get a hangover, and are just as impaired, just as over the drink-drive limit, and just as unsafe behind the wheel as you would be without it. It does not sober you up. What it changes is the pleasure that drives you to keep drinking past the limit you set yourself. Never drive after drinking, on the tablet or off it.

Most people have either no side effects or only mild ones that pass within the first couple of weeks, and the gradual build-up is designed to keep them down. If yours do not settle, there are options: nalmefene, a slower build-up, or a different approach altogether. If you are worried, message us. That is what we are here for.

The online assessment is quick. A doctor reviews it and, if naltrexone is right for you, prescribes it, dispensed and delivered to your door.

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