What Are the Side Effects of Naltrexone to Stop Drinking?
Naltrexone for alcohol use disorder commonly causes nausea, headache, dizziness, and fatigue—especially in the first few weeks.
Asking what naltrexone will actually feel like before you agree to take it is exactly the right instinct — and the honest answer is calmer than the label's long list suggests.
Here's the short version. The side effects people notice most on naltrexone are nausea, headache, dizziness, and tiredness, usually in the first days to weeks, and they often ease as the body adjusts. Serious problems are less common, and they announce themselves in recognizable ways — through the liver, through mood, or as an allergic reaction. And there's one group of people who shouldn't take naltrexone at all: anyone with opioids still in their system. The rest of this piece walks through each of those, in the order you're likely to care about them.
What do the first weeks usually feel like?
For many people, not much. For others, there's a stretch of queasiness, headaches, dizziness, or a tired, flat feeling that shows up early and then fades. The FDA label for naltrexone lists possible reactions across several categories — digestive, nervous system, sleep, mood, liver, and allergic — but the ones people tend to report first are nausea, headache, dizziness, fatigue, trouble sleeping, appetite changes, and general stomach upset.
There's no reliable timeline for when this settles, because it depends on things that differ person to person: your liver history, other medications, how much you've been drinking, even sleep and hydration. What you can count on is a useful pattern — mild effects that are slowly improving usually mean your body is adjusting, while anything that keeps getting worse is worth a call rather than a wait.
Why a medication aimed at drinking causes any of this
Because it works on the brain, not on alcohol itself. Naltrexone sits on the brain's opioid receptors — the docking sites for endorphins, your own feel-good chemicals. Part of the warm lift a drink gives you comes from endorphins landing on those receptors, and SAMHSA describes naltrexone as binding to them and blocking alcohol's rewarding effects — which is why, for some people, cravings shrink and drinking sessions get shorter. The American Academy of Family Physicians explains the same mechanism: opioid receptors appear to carry much of alcohol's pleasant effect, so blocking them makes drinking less worth it — and the medication does its best work alongside counseling and other support, not instead of it.
That last point echoes the label's own caution: naltrexone hasn't been shown to help except as part of a broader plan for managing drinking. In plain terms, it's a tool that turns down one signal in the brain. Quieting a signal your brain has leaned on for years takes adjustment, and much of what people feel in the early weeks is exactly that.
The symptoms that shouldn't wait
Most early side effects can be watched. A handful can't. Call your clinician promptly — same day, not next appointment — if you notice:
- Liver warning signs: yellowing of your skin or eyes, dark urine, pain or tenderness under your right ribs, or fatigue that keeps deepening. Naltrexone is processed by the liver, and these are the signals the label tells clinicians to watch for.
- Vomiting that won't stop — especially if you can't keep fluids down.
- Allergic signs: a spreading rash, swelling of the face or throat, trouble breathing or swallowing. If breathing is affected, that's 911, not a phone message.
- Fainting, chest pain, or severe dizziness.
- Mood changes: depression and thoughts of self-harm have been reported with naltrexone, and low mood also travels with heavy drinking itself. If you ever feel unsafe with yourself, call or text 988 first, then loop in your clinician.
None of these are common. All of them are the reason follow-up visits exist.
Who should never take it?
Anyone with opioids in their system. The label is unambiguous: naltrexone is contraindicated for people taking opioid pain medication, people dependent on opioids, people in acute opioid withdrawal, and people with a positive opioid screen. The reason is mechanical — naltrexone doesn't just block future opioids, it pushes existing ones off their receptors all at once, which can trigger sudden, severe withdrawal. If that happens, it's an emergency-room situation, not something to ride out at home. This is why a clinician will ask about every painkiller you take, including ones you only use occasionally.
Liver disease is a softer line but a real one. Because the liver does the processing, someone with acute hepatitis, liver failure, or a history of elevated liver enzymes needs an honest risk-and-monitoring conversation before starting. Pregnancy, breastfeeding, kidney problems, and mental health history round out the safety review. Full disclosure isn't a formality here — it's the thing that keeps the prescription safe.
What happens if you drink while you're on it?
Nothing dramatic — and that surprises people. Naltrexone is not disulfiram (Antabuse). Disulfiram works as a deterrent: per its FDA label, it blocks the breakdown of alcohol at the acetaldehyde stage, so drinking on it lets that toxic middle product pile up and makes you feel flushed and ill. Naltrexone does something quieter: it mutes the reward. The drink still impairs your coordination, judgment, and sleep, and still taxes your liver — it just hands back less of the lift.
That quieter mechanism is why some treatment approaches, including the Sinclair Method, involve taking naltrexone before planned drinking rather than every day, with the goal of letting the reward response fade over time. Whether daily use, targeted use, or full abstinence fits your situation is a clinician's conversation, not a self-experiment.
Make the early weeks easier on yourself
A simple record beats memory, and it makes every follow-up call faster:
- Note the start date of any symptom and whether it's improving, flat, or worsening. That trajectory is the single most useful thing you can tell a clinician.
- List everything you take — prescriptions, supplements, and any opioid exposure, however occasional.
- Separate "annoying" from "new and different." A headache that fades by afternoon is a nuisance; dark urine or yellowing eyes is a phone call.
- Say the mood part out loud. Flat, hopeless, or unsafe feelings deserve the same urgency as physical symptoms — 988 if you feel unsafe, your clinician for everything trending downward.
If naltrexone turns out not to fit
A rough first month is information, not a verdict on medication as a whole. The FDA has approved other options that work in genuinely different ways. Acamprosate doesn't touch the reward system at all — it helps rebalance the overactive "go" signaling that lingers after someone stops drinking — and it leaves the body through the kidneys rather than the liver, which is one reason it comes up when the liver is already a concern. The AAFP groups acamprosate and naltrexone as the better-supported of the approved medications and recommends pairing either one with behavioral support.
One number puts all of this in perspective. In 2024, an estimated 9.7% of Americans ages 12 and older had past-year alcohol use disorder, per NIAAA, yet only about 2.1 million of them — 7.6% — received any alcohol treatment that year. Most people never reach a medication conversation at all. That's a gap in access and awareness, not evidence the medications fail — and it means that by weighing side effects seriously, you're already further along than most people ever get.
If you don't have a clinician to take the question to, Clero can connect you with a licensed clinician by telehealth to review your health history and talk through whether naltrexone — or a different medication — deserves a place in your plan.
The side-effect list looks long because drug labels are exhaustive by design. For most people, the real experience is narrower: a few weeks of adjustment, a short list of warning signs worth knowing cold, and one hard rule about opioids. Bring an honest history, watch the right signals, and this becomes a manageable decision instead of a frightening one.
This is general education, not medical advice or a treatment plan. If you might hurt yourself, call or text 988 now. If stopping drinking brings shaking, confusion, hallucinations, or a seizure, call 911 or go to an emergency room; for confidential treatment referrals, SAMHSA's helpline is 1-800-662-HELP.
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