Schizophrenia: Nine studies (601 participants) that reported effects on symptoms and eight studies (979 participants) that reported effects on relapse were included.
CBT did not significantly reduce symptoms (SMD -0.076, 95% CI -0.235 to 0.084) or relapse (OR 1.17, 95% CI 0.88 to 1.55). Effect sizes were significantly greater in the two non-blinded studies compared to the seven blinded studies for symptoms (SMD -0.63 versus 0.00, p=0.01); there was no significant effect of blinding on relapse.
Major depression: Nine studies (563 participants) that reported effects on symptoms (Hamilton Depression Scale) and nine studies (881 participants, eight studies with blinded outcome ascertainment) that reported effects on relapse were included.
CBT significantly reduced symptoms overall (SMD -0.282, 95% CI -0.447 to -0.117), but there was no significant effect in studies with a psychosocial control. CBT significantly reduced relapse (OR 0.53, 95% CI 0.40 to 0.71). There was no significant effect of blinding on symptoms; all except one study that examined relapse were blinded.
Bipolar disorder: Four studies (487 participants), all with blinded outcome assessment, compared CBT with treatment as usual for prevention of relapse. CBT did not significantly affect relapse (OR 0.78, 95% CI 0.53 to 1.15). All studies were blinded.
Where reported, statistical heterogeneity was not significant.