Does naltrexone have antidepressant effects?

Naltrexone Does Not Improve Mood and May Worsen Depression in Susceptible Individuals

Naltrexone is not an antidepressant and should not be used to treat depression. In fact, the FDA drug label explicitly warns that depression, suicidal ideation, and suicide attempts have been reported with naltrexone use, particularly in opioid-dependent patients 1. While no causal relationship has been definitively established, this is a critical safety concern that requires monitoring.

Evidence Against Antidepressant Effects

The most recent high-quality evidence directly addressing this question comes from a 2026 randomized, double-blind, placebo-controlled trial that found low-dose naltrexone (LDN) had no effect on depressive symptoms in patients with major depressive disorder 2. At 12 weeks, depression scores improved equally in both the naltrexone group (10.5-point reduction) and placebo group (9.8-point reduction), with no significant difference between groups (p = 0.97). This study specifically tested naltrexone as an adjunctive treatment for depression and found it ineffective.

Context-Specific Findings in Substance Use Disorders

The picture becomes more nuanced when examining naltrexone's effects in patients with substance use disorders:

• In opioid-dependent patients who remain in treatment and abstinent, depression, anxiety, and anhedonia—which are elevated at baseline—typically normalize within 1-2 months regardless of whether patients receive naltrexone or placebo 3, 4. This improvement reflects recovery from substance dependence rather than a direct antidepressant effect of naltrexone.

• In depressed alcoholics, one small open-label pilot study (n=14) suggested a trend toward improvement in depressive symptoms when naltrexone was added to SSRI treatment 5. However, this was not a controlled comparison and the improvement may have resulted from reduced alcohol consumption rather than direct mood effects.

Critical Safety Warnings from FDA Drug Label

The FDA label is unequivocal about monitoring requirements 1:

• Depression, suicide attempts, and suicidal ideation have been reported in postmarketing surveillance
• Alcohol- and opioid-dependent patients taking naltrexone must be monitored for development of depression or suicidal thinking
• Families and caregivers should be alerted to watch for emergence of depression or suicidality symptoms
• No causal relationship has been proven, but the association is concerning enough to warrant explicit warnings

Mechanism Considerations

Naltrexone's pharmacology argues against antidepressant effects:

• As a μ-opioid receptor antagonist, naltrexone blocks endogenous opioid signaling, which theoretically could worsen mood in susceptible individuals
• A 2026 case report documented rapid onset of dysphoria, anhedonia, and fatigue when a patient was switched to olanzapine-samidorphan (which contains the opioid antagonist samidorphan, similar to naltrexone), with rapid resolution upon discontinuation 6
• Animal studies combining buprenorphine with naltrexone showed antidepressant-like effects 7, but this combination specifically preserves κ-opioid antagonism while reducing μ-agonism—a fundamentally different pharmacological profile than naltrexone alone

Clinical Recommendations

Do not prescribe naltrexone for mood improvement. Its approved indications are alcohol use disorder and opioid use disorder maintenance 8, 9, 10. When prescribing naltrexone for these conditions:

1. Screen for baseline depression and suicidality before initiating treatment
2. Monitor mood closely, especially in the first few months of treatment
3. Educate patients and families about the potential for mood changes and the need to report depressive symptoms immediately
4. If depression emerges, consider whether it represents:
   • Unmasking of pre-existing depression
   • A direct effect of naltrexone (discontinue if suspected)
   • Precipitated withdrawal symptoms (if opioid-free period was inadequate)

The evidence is clear: naltrexone is effective for reducing alcohol and opioid use 11, 9, 10, but it does not improve mood and requires vigilant monitoring for depressive symptoms.