Abstract: As a result of searches undertaken in 2014, we found one new study and in 2016 more data for already included studies. Five relevant studies with 1132 participants (585 are relevant to this review) are now included. All are hospital-based trials and, despite over 60 years of chlorpromazine use, have durations of less than six months and all are at least at moderate risk of bias. We found only data on low-dose (≤ 400 mg/day) versus medium-dose chlorpromazine (401 mg/day to 800 mg/day) and low-dose versus high-dose chlorpromazine (> 800 mg/day). When low-dose chlorpromazine (≤ 400 mg/day) was compared to medium-dose chlorpromazine (401 mg/day to 800 mg/day), there was no clear benefit of one dose over the other for both global and mental state outcomes (low-quality and very low-quality evidence). There was also no clear evidence for people in one dosage group being more likely to leave the study early, over the other dosage group (moderate-quality evidence). Similar numbers of participants from each group experienced agitation and restlessness (very low-quality evidence). However, significantly more people in the medium-dose group (401 mg/day to 800 mg/day) experienced extrapyramidal symptoms in the short term (2 RCTS, n = 108, RR 0.47, 95% CI 0.30 to 0.74, moderate-quality evidence). No data for death were available. When low-dose chlorpromazine (≤ 400 mg/day) was compared to high-dose chlorpromazine (> 800 mg/day), data from one study with 416 patients were available. Clear evidence of a benefit of the high dose was found with regards to global state. The low-dose group had significantly fewer people improving (RR 1.13, 95% CI 1.01 to 1.25, moderate-quality evidence). There was also a marked difference between the number of people leaving the study from each group for any reason, with significantly more people leaving from the high-dose group (RR 0.60, 95% CI 0.40 to 0.89, moderate-quality evidence). More people in the low-dose group had to leave the study due to deterioration in behaviour (RR 2.70, 95% CI 1.34 to 5.44, low-quality evidence). There was clear evidence of a greater risk of people experiencing extrapyramidal symptoms in general in the high-dose group (RR 0.43, 95% CI 0.32 to 0.59, moderate-quality evidence). One death was reported in the high-dose group yet no effect was shown between the two dosage groups (RR 0.33, 95% CI 0.01 to 8.14, moderate-quality evidence). No data for mental state were available. The dosage of chlorpromazine has changed drastically over the past 50 years with lower doses now being the preferred of choice. However, this change was gradual and arose not due to trial-based evidence, but due to clinical experience and consensus. Chlorpromazine is one of the most widely used antipsychotic drugs yet appropriate use of lower levels has come about after many years of trial and error with much higher doses. In the absence of high-grade evaluative studies, clinicians have had no alternative but to learn from experience. However, such an approach can lack scientific rigor and does not allow for proper dissemination of information that would assist clinicians find the optimum treatment dosage for their patients. In the future, data for recently released medication should be available from high-quality trials and studies to provide optimum treatment to patients in the shortest amount of time.

Plain-language summary: An updated search for relevant randomised controlled trials was run in October 2014, and again, in December 2016 and found one new study. Five studies have now been found that meet the review inclusion criteria. The included studies are all randomised, and investigate the effects of giving different doses of chlorpromazine to people with schizophrenia. The total number of participants was 585. Chlorpromazine showed different effects at varying doses. Based on weak evidence, the effects on people’s mental health at low dosage and medium dosage are much the same. However, there are more side effects at medium dose. There is more improvement in people’s mental health at high dose compared to low dose. However, side effects are much more numerous and debilitating at high dose. In the past fifty years, low dose has been the favoured amount to use with patients. This change has come about gradually and is based on everyday experience and consensus rather than hard scientific evidence. Chlorpromazine is low-cost and widely available. Despite its many side effects, chlorpromazine is likely to remain a benchmark or ‘gold standard’ drug and one of the most widely used treatments for schizophrenia worldwide. All trials in the review are hospital- based and all but one date from 20 years ago. There are a limited number of studies of limited quality and these are poorly reported and short term. Further research and trials on chlorpromazine dose are justified. Ben Gray, Senior Peer Researcher, McPin Foundation. http://mcpin.org/