What the label lists and what reports show
Naltrexone side effects
Naltrexone's FDA label lists its adverse reactions in its own words. FAERS holds 32,067 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is injection site reaction (4,417 reports).
- Generic listed
Check it at the source: the naltrexone FDA label on DailyMed (effective September 4, 2026); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of VIVITROL?VIVITROL can cause serious side effects, including: See “ What is the most important information I should know about VIVITROL? ” Depressed mood. Sometimes this leads to suicide, or suicidal thoughts, and suicidal behavior. Tell your family members and people closest to you that you are taking VIVITROL. You, a family member, or the people closest to you should call your healthcare provider right away if you become depressed or have any of the following symptoms of depression, especially if they are new, worse, or worry you: You feel sad or have crying spells. You are no longer interested in seeing your friends or doing things you used to enjoy. You are sleeping a lot more or a lot less than usual. You feel hopeless or helpless. You are more irritable, angry, or aggressive than usual. You are more or less hungry than usual or notice a big change in your body weight. […]
Source: FDA drug label (VIVITROL), Alkermes, Inc., effective May 31, 2026 (SPL set cd11c435-b0f0-4bb9-ae78-60f101f3703f), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsDuring two randomized, double-blind placebo-controlled 12-week trials to evaluate the efficacy of naltrexone hydrochloride as an adjunctive treatment of alcohol dependence, most patients tolerated naltrexone hydrochloride well. In these studies, a total of 93 patients received naltrexone hydrochloride at a dose of 50 mg once daily. Five of these patients discontinued naltrexone hydrochloride because of nausea. No serious adverse events were reported during these two trials. While extensive clinical studies evaluating the use of naltrexone hydrochloride in detoxified, formerly opioid-dependent individuals failed to identify any single, serious untoward risk of naltrexone hydrochloride use, placebo-controlled studies employing up to five-fold higher doses of naltrexone hydrochloride (up to 300 mg per day) than that recommended for use in opiate receptor blockade have shown that naltrexone …
Table 2: Treatment-emergent Clinical Adverse Events (Events in ≥2% of patients with opioid dependence treated with VIVITROL and occurring more frequently in the VIVITROL group than in the placebo group)
This table is printed in the VIVITROL label published by Alkermes, Inc. of May 31, 2026; the label quoted above does not print one.
| Reaction | Body System n | Adverse Event / Preferred Term % | Placebo N=124 n | VIVITROL 380 mg N=126 % |
|---|---|---|---|---|
| Alanine aminotransferase increased | 7 | 6 | 16 | 13 |
| Nasopharyngitis | 3 | 2 | 9 | 7 |
| Insomnia | 1 | 1 | 8 | 6 |
| Hypertension | 4 | 3 | 6 | 5 |
| Injection site pain | 1 | 1 | 6 | 5 |
| Toothache | 2 | 2 | 5 | 4 |
| Headache | 3 | 2 | 4 | 3 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
Source: FDA drug label, SpecGx LLC, effective September 4, 2026 (SPL set 06ff2d5a-e62b-4fa4-bbdb-01938535bc65), via openFDA; the full label on DailyMed
What do FAERS reports show?
32,067 reports list naltrexone among the medicines taken, each a report of something that happened, not proof the medicine caused it; 1,395 are coded as a death and 4,356 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 23 reactions below, 14 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Naltrexone: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions