Randomized, proof-of-concept trial of low dose naltrexone for patients with breakthrough symptoms of major depressive disorder on antidepressants.

•Low-dose naltrexone is thought to function via a dopaminergic mechanism that may have potential antidepressant effects.•In 12 depressed subjects who relapsed on pro-dopaminergic antidepressants, low dose naltrexone reduced depression severity.•Low-dose naltrexone augmentation may be effective for depressive relapse, but the findings must be interpreted with caution.