Short answer: In the label's open-label safety study of about 570 people treated for alcoholism, the most common new side effects were nausea (10%), headache (7%), dizziness, nervousness and fatigue (4% each), trouble sleeping and vomiting (3%), and anxiety and sleepiness (2%). Naltrexone tablets have no boxed warning; the label warns about opioid overdose after stopping, sudden opioid withdrawal and liver injury.
What Naltrexone is approved for: Naltrexone tablets are approved to treat alcohol dependence and to block the effects of opioids taken from outside the body (Indications and Usage). The label says they have not been shown to provide any benefit except as part of an appropriate plan of management for the addictions.
Source
Naltrexone Hydrochloride Tablets, USP 50 mg, prescribing information. SpecGx LLC (Par Health). DailyMed, version published September 9, 2026. DailyMed setid 06ff2d5a-e62b-4fa4-bbdb-01938535bc65
No. The current Naltrexone label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Naltrexone.
| Event | Naltrexone | Placebo |
|---|---|---|
| Depression | 0 to 15% | 0 to 17% |
| Suicide Attempt/Ideation | 0 to 1% | 0 to 3% |
Rates of new depression and suicide attempt or ideation across groups treated for alcoholism. The label says no causal relationship with naltrexone is suspected, but that naltrexone does not reduce the risk of suicide in these patients.
Open-label safety study, about 570 people with alcoholism, new side effects in 2% or more: nausea 10%, headache 7%, dizziness 4%, nervousness 4%, fatigue 4%, insomnia 3%, vomiting 3%, anxiety 2%, somnolence 2%.
In two 12-week placebo-controlled alcohol dependence trials, 93 people took 50 mg once daily; 5 stopped because of nausea, and no serious adverse events were reported.
Reported at both baseline and during opioid addiction trials in more than 10%: difficulty sleeping, anxiety, nervousness, abdominal pain or cramps, nausea and/or vomiting, low energy, joint and muscle pain, and headache. Under 10%: loss of appetite, diarrhea, constipation, thirst, irritability, dizziness, rash, delayed ejaculation, decreased potency and chills.
At about five times the recommended dose (300 mg per day) in obese subjects, 19% (5 of 26) on naltrexone vs 0% (0 of 24) on placebo developed liver enzyme (transaminase) elevations after 3 to 8 weeks; levels returned toward baseline within weeks.
A small fraction of people may get an opioid withdrawal-like set of symptoms: tearfulness, mild nausea, abdominal cramps, restlessness, bone or joint pain, muscle aches and nasal symptoms.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Who should not take it. People taking opioid pain medicines, people currently dependent on opioids (including those on methadone or buprenorphine), people in acute opioid withdrawal, anyone who failed the naloxone challenge test or has a positive urine screen for opioids, and anyone with a past sensitivity to naltrexone.
Opioid overdose risk. After naltrexone is stopped, people may respond to lower doses of opioids than before, and fatal overdoses have been reported after treatment ended. Trying to overcome the blockade with large amounts of opioids may lead to life-threatening intoxication or fatal overdose. The label says to discuss having an opioid overdose reversal agent such as naloxone or nalmefene available.
Sudden (precipitated) opioid withdrawal. In someone still dependent on opioids, naltrexone can trigger withdrawal severe enough for hospital or intensive care, usually within 5 minutes and lasting up to 48 hours. An opioid-free interval of at least 7 to 10 days is recommended after short-acting opioids, and people coming off buprenorphine or methadone may be vulnerable for as long as 2 weeks.
Liver injury. Cases of hepatitis and clinically significant liver problems have been seen. Naltrexone is stopped if symptoms or signs of acute hepatitis appear. Higher doses caused liver cell injury in a substantial share of people.
Depression and suicidal thoughts. Depression, suicide, suicide attempts and suicidal thoughts have been reported after approval in people treated for opioid dependence; no causal link has been shown. The label says to watch for them.
Ultra rapid opioid detox. Safe use in ultra rapid opiate detoxification programs has not been established; withdrawal symptoms and deaths of unknown cause have been reported there.
Opioid-containing medicines and pain care. People on naltrexone may not get the expected effect from opioid pain, cough or diarrhea medicines. If opioids are needed in an emergency, larger amounts may be needed and breathing may be slowed more deeply and for longer, so close monitoring is required.
Kidney and liver impairment. Caution is recommended with kidney impairment. Naltrexone exposure was about 5 times higher with compensated and 10 times higher with decompensated liver cirrhosis.
From the Information for Patients section of the prescribing information that comes with Naltrexone:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.