Acamprosate vs. Naltrexone: A Comparison for Alcohol Use

Acamprosate and naltrexone are both FDA-approved medications for alcohol use disorder, but they work through different brain systems and tend to help different aspects of the problem. A large meta-analysis found that acamprosate is better at helping people stay completely abstinent, while naltrexone is better at reducing heavy drinking and curbing cravings.¹ That distinction matters more than it sounds, because which one fits you better depends on your drinking pattern, your treatment goal, your body’s health, and possibly even your genetics.

How Each Medication Works

Naltrexone is an opioid antagonist. It blocks the mu-opioid receptors in the brain that are part of the reward pathway activated by alcohol. The idea is straightforward: if alcohol no longer triggers the same pleasurable rush, you are less motivated to keep drinking or to drink heavily.² People on naltrexone often describe feeling indifferent to alcohol rather than repulsed by it. A drink just doesn’t deliver the payoff it used to.

Acamprosate targets a completely different system. Chronic heavy drinking disrupts glutamate signaling in the brain, leaving the nervous system in a hyperexcitable state once drinking stops. That overactivity contributes to anxiety, restlessness, insomnia, and the nagging urge to drink just to feel normal again. Acamprosate works by restoring more normal glutamate transmission and may also influence GABA-related signaling, essentially calming the neurochemical chaos that abstinence exposes.³⁴

Because they act on separate pathways, combining the two is biologically plausible, and some clinicians do prescribe them together. The largest U.S. trial to test that idea, the COMBINE study, enrolled over 1,300 participants across multiple sites and tested naltrexone, acamprosate, or both in various configurations alongside behavioral interventions.⁵ The combination did not clearly outperform naltrexone alone in that particular trial, which tempered enthusiasm for routine dual prescribing, though many addiction specialists still consider it for patients who don’t respond adequately to one medication.

Which One Works Better, and for Whom

The short answer is that neither is universally superior. They shine on different outcomes. The meta-analysis that compared them head-to-head across dozens of trials found acamprosate had a meaningfully larger effect on maintaining complete abstinence, while naltrexone had a larger effect on reducing heavy drinking days and cravings.¹ That pattern makes pharmacological sense: acamprosate soothes the brain state that makes staying sober feel unbearable, so it helps people who have already stopped drinking maintain that state. Naltrexone blunts the rewarding buzz, so it helps people who are still drinking cut back or avoid binges.

A 2023 systematic review and meta-analysis put some concrete numbers on the comparison. To prevent one person from returning to any drinking, you would need to treat about 11 people with acamprosate or about 18 people with oral naltrexone at the standard 50 mg daily dose. For preventing return to heavy drinking specifically, naltrexone’s number needed to treat was about 11.⁶ Those numbers might not sound dramatic, but they compare favorably to medications used for many other chronic conditions, and they represent real people whose lives improve.

One consistent finding in the acamprosate literature is that it works best when patients have already been through detoxification before starting the medication. Trials that required a period of abstinence before enrollment showed substantially larger effect sizes for acamprosate than trials that did not.¹ For naltrexone, requiring abstinence before the trial was also associated with better outcomes for both abstinence maintenance and reduced heavy drinking, but naltrexone is more commonly initiated while a person is still drinking. That flexibility is a practical advantage in settings where waiting for full detoxification is not realistic.

Reward Drinkers Versus Relief Drinkers

An influential framework in addiction medicine divides people with alcohol use disorder into two broad groups based on what drives their drinking. “Reward drinkers” drink primarily for the pleasurable, euphoric effects. They tend to drink in social situations, enjoy the buzz, and find alcohol positively reinforcing. “Relief drinkers” drink mainly to escape negative feelings: anxiety, tension, irritability, or the physical discomfort of withdrawal. Their drinking is driven by a desire to feel less bad rather than a desire to feel good.⁷

The hypothesis follows logically from the mechanisms: naltrexone, which blocks the opioid-mediated reward from alcohol, should help reward drinkers more, while acamprosate, which calms the glutamate-driven hyperexcitability underlying withdrawal distress, should help relief drinkers more.⁸ The PREDICT trial was designed specifically to test this idea, assigning patients to naltrexone or acamprosate based on whether they were categorized as reward or relief drinkers.⁹

The results have been mixed. Some neuroimaging evidence supports the basic premise. In one study, patients who showed strong brain activation in the ventral striatum (a reward-processing region) when shown alcohol-related images responded better to naltrexone than to acamprosate.¹⁰ But the clinical evidence for neatly sorting patients into reward and relief categories and prescribing accordingly has not been as clean as researchers hoped. In practice, most people drink for a mixture of reasons that shifts over time, making the classification less tidy than it sounds on paper. The framework remains useful as a conceptual guide, but it is not yet a reliable clinical tool for choosing between the two medications.

Genetics and Naltrexone Response

One of the more promising avenues for choosing between these medications involves a specific genetic variant in the mu-opioid receptor gene, called OPRM1. People who carry a particular version of this gene (the Asp40 or “G” allele) appear to respond better to naltrexone than people who carry the more common version. Analysis from the COMBINE trial confirmed that this genetic variant predicted naltrexone treatment response.¹¹

A systematic review and meta-analysis looking across studies found that naltrexone-treated patients carrying the G allele had roughly twice the odds of avoiding relapse compared to those without it.¹² That is a meaningful difference. In theory, a simple genetic test could help identify people most likely to benefit from naltrexone. In practice, this kind of pharmacogenomic testing is not yet routine in addiction treatment settings, though it is slowly becoming more available. No equivalent genetic marker has been identified for predicting acamprosate response, so at the moment, the genetic matching story is one-sided.

Day-to-Day Practicalities

The dosing difference between the two medications is substantial and affects adherence in real-world treatment. Naltrexone is taken as a single 50 mg pill once a day. Acamprosate requires two pills three times a day, for a total of six pills daily.⁶ For anyone who has struggled with a medication that needs to be taken multiple times a day, the adherence challenge of acamprosate is obvious. Forgetting a midday dose while at work, skipping the evening dose when social plans run late, or simply getting fatigued by the routine are all common obstacles. Naltrexone also comes in an extended-release injectable form (marketed as Vivitrol) given once a month, which eliminates the daily pill altogether, though it costs more and requires a clinic visit for each injection.

Side effects differ in character. Naltrexone’s most common complaints are nausea, headache, dizziness, and fatigue, especially in the first few days. Some people feel generally unwell or experience a low mood. Acamprosate’s side effect profile leans more toward gastrointestinal issues, particularly diarrhea, along with headache and insomnia. Neither medication is considered especially hard to tolerate by the standards of psychiatric prescribing, but the specific side effects can make one a better fit than the other for a given person.¹³

Liver Disease and Other Medical Considerations

This is where the choice between the two often becomes less about preference and more about medical necessity. Acamprosate is processed by the kidneys, not the liver, which makes it the default choice for patients with significant liver disease. It should be avoided in people with severe kidney impairment. Naltrexone is metabolized by the liver, and for years clinicians avoided it in patients with liver problems. That caution was based on older studies using very high doses, and the thinking has shifted considerably. Recent evidence indicates that naltrexone at the standard dose is safe in patients with liver disease, including cirrhosis, and previous concerns about liver toxicity have not been borne out.¹⁴ Still, some prescribers remain cautious, and monitoring liver function during treatment is a common practice.

One absolute contraindication for naltrexone is concurrent use of opioids. Because naltrexone blocks opioid receptors, giving it to someone who is physically dependent on opioids can trigger acute withdrawal, which is dangerous and extremely unpleasant. People who need opioid pain medication for an injury or chronic condition generally cannot take naltrexone. Acamprosate has no such interaction, making it the clear choice for patients who also use opioids for legitimate medical purposes.¹⁵

Cost-Effectiveness and the Underprescribing Problem

Both acamprosate and naltrexone are available as generics and are relatively inexpensive compared to many chronic-disease medications. A cost-effectiveness analysis focused on patients with alcohol-related cirrhosis found that both medications cost less and provided more quality-adjusted years of life than other interventions studied.¹⁶ That finding makes the low rates of prescribing particularly frustrating. Despite strong evidence that these medications help, they remain dramatically underused. A study of prescribing patterns in Australian Aboriginal Community Controlled Health Services found that fewer than 1 in 500 patients with alcohol-related health concerns received a prescription for any relapse prevention medication, with acamprosate and naltrexone prescribed in roughly equal numbers.¹⁷

This is not a uniquely Australian problem. Studies in the United States consistently show that only a small fraction of people who could benefit from these medications actually receive them. The barriers are multiple: many primary care providers feel undertrained in addiction medicine, some patients do not realize medications exist for alcohol problems, and the lingering stigma around treating addiction pharmacologically (as opposed to relying solely on willpower or therapy) still influences both clinician and patient attitudes. The evidence strongly suggests that more people would benefit if these medications were prescribed more freely.

When Neither Medication Works

Not everyone responds to naltrexone or acamprosate, and for those who don’t, options exist. The American Psychiatric Association’s guidelines note that topiramate or gabapentin can be offered to patients with moderate to severe alcohol use disorder who prefer those medications, cannot tolerate naltrexone and acamprosate, or have not responded to them.¹⁸ Disulfiram (Antabuse) is another FDA-approved option, though it works through a different principle entirely: it makes you physically ill if you drink, acting as a deterrent rather than reducing the urge to drink. Its effectiveness depends heavily on someone being willing to take it, which limits its use.

Topiramate has accumulated a reasonable evidence base for reducing heavy drinking days and is increasingly used off-label. Gabapentin may help particularly with sleep disturbances and anxiety during early recovery. Neither has the same depth of evidence behind it as naltrexone or acamprosate, but they give clinicians and patients more tools to work with when first-line options fall short.

The Posttreatment Question

One practical issue that comes up for anyone starting either medication is how long to stay on it. Guidelines typically recommend a minimum of three to six months, with many clinicians recommending a year or longer. The COMBINE study followed participants for a year after the 16-week active treatment period ended and examined whether the benefits held.¹⁹ The results highlighted a common tension in addiction treatment: medications tend to work while you take them, and the benefits can fade after stopping. This is not a sign that the medications “failed” any more than blood pressure rising after stopping an antihypertensive means that drug failed. Alcohol use disorder is a chronic condition, and many patients benefit from extended or even indefinite treatment.

Deciding when or whether to taper off involves weighing the stability of a person’s recovery, their coping strategies, their support network, and their personal preference. Some people stay on naltrexone for years and find the security it provides worth the minor inconvenience. Others use acamprosate through the difficult first year and then discontinue once the neurobiological recovery from chronic drinking has had time to stabilize. There is no single right answer.

How Medications Fit with Therapy and Support Programs

Neither acamprosate nor naltrexone is meant to be used in isolation. Both work best when combined with some form of psychosocial support, whether that is formal therapy (cognitive-behavioral therapy, motivational interviewing), mutual aid groups, or structured medical management. The COMBINE study tested this directly by pairing medications with different levels of behavioral support and found that even brief, structured medical visits improved outcomes.⁵ The medications handle the neurochemical piece; therapy and social support handle the behavioral, emotional, and environmental pieces. People who approach treatment as an either/or choice between medication and therapy are working with an incomplete toolkit.

This point is worth emphasizing because of a persistent cultural divide in alcohol treatment. Some treatment programs remain philosophically opposed to medication, viewing it as a crutch or a substitute for the “real work” of recovery. The evidence does not support that position. Medications like naltrexone and acamprosate address measurable brain changes caused by chronic alcohol exposure, and using them alongside behavioral approaches consistently produces better outcomes than either alone.