Abstract: We included 28 trials with 8487 participants on five SGAs: amisulpride, aripiprazole, olanzapine, quetiapine and risperidone. Three studies (1092 participants) provided data on aripiprazole augmentation in MDD. All efficacy data (response n = 1092, three RCTs, OR 0.48; 95% CI 0.37 to 0.63), (MADRS n = 1077, three RCTs, MD -3.04; 95% CI -4.09 to -2) indicated a benefit for aripiprazole but  more side effects (weight gain, EPS) . Seven trials (1754 participants) reported data on olanzapine. Compared to placebo fewer people discontinued treatment due to inefficacy; compared to antidepressants there were no efficacy differences, olanzapine augmentation showed symptom reduction (MADRS n = 808, five RCTs, MD -2.84; 95% CI -5.48 to -0.20), but also more weight or prolactin increase. Quetiapine data are based on seven trials (3414 participants). Compared to placebo, quetiapine monotherapy (response n = 1342, three RCTs, OR 0.52; 95% CI 0.41 to 0.66) and quetiapine augmentation (response n = 937, two RCTs, OR 0.68; 95% CI 0.52 to 0.90) showed symptom reduction, but quetiapine induced more sedation. Four trials (637 participants) presented data on risperidone augmentation, response data were better for risperidone (n = 371, two RCTs, OR 0.57; 95% CI 0.36 to 0.89) but augmentation showed more prolactin increase and weight gain. Five studies (1313 participants) presented data on amisulpride treatment for dysthymia. There were some beneficial effects compared to placebo or antidepressants but tolerability was worse. Quetiapine was more effective than placebo treatment. Aripiprazole and quetiapine and partly also olanzapine and risperidone augmentation showed beneficial effects compared to placebo. Some evidence indicated beneficial effects of low-dose amisulpride for dysthymic people. Most SGAs showed worse tolerability.

Plain-language summary: This review found 28 studies on five second-generation antipsychotic drugs (amisulpride, aripiprazole, olanzapine, quetiapine and risperidone) comparing the effects of the drugs alone or adding them or placebo to antidepressants for major depressive disorder and dysthymia. There is evidence that amisulpride might lead to symptom reduction in dysthymia, while no important differences were seen for major depression. There is limited evidence that aripiprazole leads to symptom reduction when added to antidepressants. Olanzapine had no beneficial effects for treatment of depression when compared to antidepressants or compared to placebo but there was limited evidence for the benefits of olanzapine as additional treatment. Data on quetiapine indicated beneficial effects for quetiapine alone or as additional treatment when compared to placebo; data on quetiapine versus duloxetine did not show beneficial effects in terms of symptom reduction for either group, but quetiapine treatment was less well tolerated. The data, however, are very limited. Slight benefits of risperidone as additional treatment, in terms of symptom reduction, are also based on a rather small number of randomised participants. Generally, treatment with second-generation antipsychotic drugs was associated with worse tolerability, mainly due to sedation, weight gain or laboratory values such as prolactin increase.