Selective serotonin reuptake inhibitors (SSRIs) are the preferred pharmacological treatment for obsessive–compulsive disorder (OCD). However, insufficient response is common and it remains unclear whether specific patient-level factors influence the likelihood of treatment response.

To determine the efficacy and acceptability of SSRIs in adult OCD, and to identify patient-level modifiers of efficacy.

We conducted an individual patient data meta-analysis (IPDMA) of industry-sponsored short-term, randomised, placebo-controlled SSRI trials submitted for approval to the Dutch regulatory agency to obtain marketing approval for treating OCD in adults. We performed a two-stage meta-analysis, using crude data of available trials. The primary outcome was the difference in Yale–Brown Obsessive–Compulsive Scale (YBOCS) change between active treatment and placebo. Secondary outcomes were differences in response (defined as the odds ratio of ≥35% YBOCS point reduction) and acceptability (defined as the odds ratio for all-cause discontinuation). We examined the modifying effect of baseline characteristics: age, gender, illness severity, depressive symptoms, weight, illness duration and history of antidepressant use.

After excluding three trials because of missing data, we analysed results from 11 trials (79% of all submitted trials, n = 2372). The trial duration ranged from 10 to 13 weeks. Mean difference of SSRIs relative to placebo was 2.65 YBOCS points (95% CI 1.85–3.46, p < 0.0001), equalling a small effect size (0.33 Hedges’ g). The odds ratio for response was 2.21 in favour of active treatment (95% CI 1.72–2.83, p < 0.0001), with a number needed to treat of seven. Patient characteristics did not modify symptom change or response. Acceptability was comparable for SSRIs and placebo.

Our IPDMA showed that SSRIs are well accepted and superior to placebo for treating OCD. The effects are modest and independent of baseline patient characteristics.

Little is known about the effect of ethnicity on the response to antipsychotic medication in patients with schizophrenia.

To determine whether ethnicity moderates the response to antipsychotic medication in patients with schizophrenia, and whether this moderation is independent of confounders.

We analysed 18 short-term, placebo-controlled registration trials of atypical antipsychotic medications in patients with schizophrenia (N = 3880). A two-step, random-effects, individual patient data meta-analysis was applied to establish the moderating effect of ethnicity (White versus Black) on symptom improvement according to the Brief Psychiatric Rating Scale (BPRS) and on response, defined as >30% BPRS reduction. These analyses were corrected for baseline severity, baseline negative symptoms, age and gender. A conventional meta-analysis was performed to determine the effect size of antipsychotic treatment for each ethnic group separately.

In the complete data-set, 61% of patients were White, 25.6% of patients were Black and 13.4% of patients were of other ethnicities. Ethnicity did not moderate the efficacy of antipsychotic treatment: pooled β-coefficient for the interaction between treatment and ethnic group was −0.582 (95% CI −2.567 to 1.412) for mean BPRS change, with an odds ratio of 0.875 (95% CI 0.510–1.499) for response. These results were not modified by confounders.

Atypical antipsychotic medication is equally effective in both Black and White patients with schizophrenia. In registration trials, White and Black patients were overrepresented relative to other ethnic groups, limiting the generalisability of our findings.