Background: Acute psychotic illness, especially when associated with agitated or violent behaviour, can require urgent pharmacological tranquillisation or sedation. In several countries, clinicians often use benzodiazepines (either alone or in combination with antipsychotics) for this outcome. Objectives: To estimate the effects of benzodiazepines, alone or in combination with antipsychotics, when compared with placebo or antipsychotics, alone or in combination with antihistamines, to control disturbed behaviour and reduce psychotic symptoms. Search methods: We searched the Cochrane Schizophrenia Group's register (January 2012), inspected reference lists of included and excluded studies and contacted authors of relevant studies. Selection criteria: We included all randomised clinical trials (RCTs) comparing benzodiazepines alone or in combination with any antipsychotics, versus antipsychotics alone or in combination with any other antipsychotics, benzodiazepines or antihistamines, for people with acute psychotic illnesses. Data collection and analysis: We reliably selected studies, quality assessed them and extracted data. For binary outcomes, we calculated standard estimates of relative risk (RR) and their 95% confidence intervals (CI) using a fixed-effect model. For continuous outcomes, we calculated the mean difference (MD) between groups. If heterogeneity was identified, this was explored using a random-effects model. Main results: We included 21 trials with a total of n = 1968 participants. There was no significant difference for most outcomes in the one trial that compared benzodiazepines with placebo, although there was a higher risk of no improvement in people receiving placebo in the medium term (one to 48 hours) (n = 102, 1 RCT, RR 0.62, 95% CI 0.40 to 0.97, very low quality evidence). There was no difference in the number of participants who had not improved in the medium term when benzodiazepines were compared with antipsychotics (n = 308, 5 RCTs, RR 1.10, 95% CI 0.85 to 1.42, low quality evidence); however, people receiving benzodiazepines were less likely to experience extrapyramidal effects (EPS) in the medium term (n = 536, 8 RCTs, RR 0.15, 95% CI 0.06 to 0.39, moderate quality of evidence). Data comparing combined benzodiazepines and antipsychotics versus benzodiazepines alone did not yield any significant results. When comparing combined benzodiazepines/antipsychotics (all studies compared haloperidol) with the same antipsychotics alone (haloperidol), there was no difference between groups in improvement in the medium term (n = 155, 3 RCTs, RR 1.27, 95% CI 0.94 to 1.70, very low quality evidence) but sedation was more likely in people who received the combination therapy (n = 172, 3 RCTs, RR 1.75, 95% CI 1.14 to 2.67, very low quality evidence). However, more participants receiving combined benzodiazepines and haloperidol had not improved by medium term when compared to participants receiving olanzapine (n = 60,1 RCT, RR 25.00, 95% CI 1.55 to 403.99, very low quality evidence) or ziprasidone (n = 60, 1 RCT, RR 4.00, 95% CI 1.25 to 12.75 very low quality evidence). When haloperidol and midazolam were compared with olanzapine, there was some evidence the combination was superior in terms of improvement, sedation and behaviour. Authors' conclusions: The evidence from trials for the use of benzodiazepines alone is not good. There were relatively little good data and most trials are too small to highlight differences in either positive or negative effects. Adding a benzodiazepine to other drugs does not seem to confer clear advantage and has potential for adding unnecessary adverse effects. Sole use of older antipsychotics unaccompanied by anticholinergic drugs seems difficult to justify. Much more high quality research is needed in this area.