Naltrexone 50 mg is an oral medication FDA-approved for two conditions: alcohol use disorder and opioid use disorder. It works by blocking opioid receptors in the brain, which dulls the rewarding effects of both alcohol and opioids. This makes it easier to reduce drinking or stay off opioids after detox. The 50 mg tablet is the standard daily maintenance dose, sold under the brand name Revia.
How It Works in the Brain
Your brain has opioid receptors that play a central role in pleasure and reward. When you drink alcohol, your body releases natural opioids that activate these receptors, producing a feel-good response. Naltrexone parks itself on those receptors and blocks the signal. As an opioid antagonist, it doesn’t produce any high or sedation on its own. It simply prevents the reward loop from firing the way it normally would.
For alcohol, this means drinking feels less satisfying. The buzz is muted. Over time, the association between alcohol and pleasure weakens. For opioids, the blocking effect is even more direct: if someone takes an opioid while on naltrexone, they won’t feel the expected euphoria, which removes a major incentive to use.
Treating Alcohol Use Disorder
Naltrexone at 50 mg daily is one of the most studied medications for reducing heavy drinking. Clinical trials have shown it reduces binge drinking days, total number of drinks consumed, and cravings. The 50 mg dose is the one used in most clinical practice and in the major trials that established its effectiveness.
Some prescribers use what’s called the Sinclair Method, where naltrexone is taken one hour before drinking rather than every day. Neuroscientist John Sinclair found that taking naltrexone specifically before drinking gradually weakens the brain’s learned connection between alcohol and reward. This approach may be particularly helpful for binge drinkers. Either way, the goal is the same: make alcohol less reinforcing so that cravings fade over time.
Treatment guidelines from SAMHSA recommend continuing naltrexone for at least 6 to 12 months. Research supports this timeline. A 2022 review of studies involving 1,500 patients found that treatment lasting longer than three months reduced heavy drinking days by nearly two days per month compared to shorter courses. A separate 2023 study of over 9,000 patients with alcohol-related liver disease found that those who stayed on naltrexone for 3 to 12 months had significantly better survival rates than those who received no medication. Since relapse risk remains high throughout the first year, staying on treatment for at least 12 months is often recommended.
Preventing Opioid Relapse
The other FDA-approved use for naltrexone 50 mg is preventing relapse in people who have already gone through opioid detox. It’s not a treatment for active opioid addiction or withdrawal. Instead, it’s a maintenance medication that helps people stay off opioids by blocking the high they would otherwise feel.
Starting naltrexone after opioid use requires careful timing. You need to be completely opioid-free for a minimum of 7 to 10 days if you were using short-acting opioids like heroin or oxycodone. People transitioning from longer-acting opioids like methadone or buprenorphine may need to wait at least two weeks. If naltrexone is started too soon, it can trigger precipitated withdrawal, a sudden and intense onset of withdrawal symptoms caused by the medication rapidly displacing opioids from the brain’s receptors.
To reduce this risk, treatment typically starts with a smaller 25 mg dose on the first day. If no withdrawal symptoms appear, the full 50 mg daily dose begins the next day.
What Naltrexone Does Not Do
Naltrexone is not a painkiller, not a sedative, and not addictive. It produces no high and has no abuse potential. It also does not treat withdrawal symptoms. It’s purely a blocking agent, which means it works best for people who have already stabilized and are focused on staying in recovery.
One critical safety point: naltrexone blocks opioid medications along with recreational opioids. If you need emergency pain relief or surgery while taking naltrexone, standard opioid painkillers won’t work as expected. Carrying a card or wearing a medical alert bracelet noting that you take naltrexone is a practical step so emergency providers can use alternative pain management approaches.
Liver Health and Monitoring
Naltrexone is processed by the liver, and high doses have been associated with liver stress. For most people at the standard 50 mg dose, serious liver problems are uncommon, but periodic liver function monitoring is standard practice during treatment. People with compensated cirrhosis (stable liver disease) can generally use naltrexone with close monitoring. Those with severe, decompensated liver disease should avoid it.
Common Side Effects
The most frequently reported side effects are nausea, headache, dizziness, fatigue, and difficulty sleeping. Nausea is the most common and tends to be worst in the first few days before the body adjusts. Starting at the lower 25 mg dose on day one helps reduce this. Most side effects are mild and improve within the first week or two of treatment.
50 mg vs. Low-Dose Naltrexone
If you’ve come across “low-dose naltrexone” or “LDN” online, that’s a different use entirely. LDN refers to naltrexone taken at 1 to 5 mg, a fraction of the standard dose. At these tiny amounts, the medication is being explored for chronic pain and inflammatory conditions like fibromyalgia, multiple sclerosis, complex regional pain syndrome, rheumatoid arthritis, and Crohn’s disease. The theory is that very low doses briefly block opioid receptors, which triggers the body to upregulate its own natural pain-relieving and anti-inflammatory responses.
LDN is not FDA-approved for any of these conditions and is considered off-label. The 50 mg dose, by contrast, is the established, FDA-approved formulation specifically designed for alcohol and opioid use disorders. These are fundamentally different treatment strategies that happen to use the same molecule at very different amounts.