The lifetime prevalence of schizophrenia is approximately 0.7% and incidence rates vary between 7.7 and 43.0 per 100,000; about 75% of people have relapses and continued disability, and one third fail to respond to standard treatment. Positive symptoms include auditory hallucinations, delusions, and thought disorder. Negative symptoms (demotivation, self-neglect, and reduced emotion) have not been consistently improved by any treatment.
Methods and outcomes
We conducted a systematic review and aimed to answer the following clinical questions: What are the effects of drug treatments for positive, negative, or cognitive symptoms of schizophrenia? What are the effects of drug treatments in people with schizophrenia who are resistant to standard antipsychotic drugs? What are the effects of interventions to improve adherence to antipsychotic medication in people with schizophrenia? We searched: Medline, Embase, The Cochrane Library, and other important databases up to May 2010 (Clinical Evidence reviews are updated periodically; please check our website for the most up-to-date version of this review). We included harms alerts from relevant organisations such as the US Food and Drug Administration (FDA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA).
We found 51 systematic reviews, RCTs, or observational studies that met our inclusion criteria. We performed a GRADE evaluation of the quality of evidence for interventions.
In this systematic review, we present information relating to the effectiveness and safety of the following interventions: amisulpride, chlorpromazine, clozapine, depot haloperidol decanoate, haloperidol, olanzapine, pimozide, quetiapine, risperidone, sulpiride, ziprasidone, zotepine, aripiprazole, sertindole, paliperidone, flupentixol, depot flupentixol decanoate, zuclopenthixol, depot zuclopenthixol decanoate, behavioural therapy, clozapine, compliance therapy, first-generation antipsychotic drugs in treatment-resistant people, multiple-session family interventions, psychoeducational interventions, and second-generation antipsychotic drugs in treatment-resistant people.
The lifetime prevalence of schizophrenia is approximately 0.7% and incidence rates vary between 7.7 and 43.0 per 100,000; about 75% of people have relapses and continued disability, and one third fail to respond to standard treatment.
Positive symptoms include auditory hallucinations, delusions, and thought disorder. Negative symptoms (anhedonia, asociality, flattening of affect, and demotivation) and cognitive dysfunction have not been consistently improved by any treatment.
Standard treatment of schizophrenia has been antipsychotic drugs, the first of which included chlorpromazine and haloperidol, but these so-called first-generation antipsychotics can all cause adverse effects such as extrapyramidal adverse effects, hyperprolactinaemia, and sedation. Attempts to address these adverse effects led to the development of second-generation antipsychotics.
The second-generation antipsychotics amisulpride, clozapine, olanzapine, and risperidone may be more effective at reducing positive symptoms compared with first-generation antipsychotic drugs, but may cause similar adverse effects, plus additional metabolic effects such as weight gain.
CAUTION: Clozapine has been associated with potentially fatal blood dyscrasias. Blood monitoring is essential, and it is recommended that its use be limited to people with treatment-resistant schizophrenia.
Pimozide, quetiapine, aripiprazole, sulpiride, ziprasidone, and zotepine seem to be as effective as standard antipsychotic drugs at improving positive symptoms. Again, these drugs cause similar adverse effects to first-generation antipsychotics and other second-generation antipsychotics.
CAUTION: Pimozide has been associated with sudden cardiac death at doses above 20 mg daily.
We found very little evidence regarding depot injections of haloperidol decanoate, flupentixol decanoate, or zuclopenthixol decanoate; thus, we don’t know if they are more effective than oral treatments at improving symptoms.
In people who are resistant to standard antipsychotic drugs, clozapine may improve symptoms compared with first-generation antipsychotic agents, but this benefit must be balanced against the likelihood of adverse effects.
We found limited evidence on other individual first- or second-generation antipsychotic drugs other than clozapine in people with treatment-resistant schizophrenia.In people with treatment-resistant schizophrenia, we don't know how second-generation agents other than clozapine compare with each other or first-generation antipsychotic agents, or how clozapine compares with other second-generation antipsychotic agents, because of a lack of evidence.
We don't know whether behavioural interventions, compliance therapy, psychoeducational interventions, or family interventions improve adherence to antipsychotic medication compared with usual care because of a paucity of good-quality evidence.
It is clear that some included studies in this review have serious failings and that the evidence base for the efficacy of antipsychotic medication and other interventions is surprisingly weak. For example, although in many trials haloperidol has been used as the standard comparator, the clinical trial evidence for haloperidol is less impressive may be expected.
By their very nature, systematic reviews and RCTs provide average indices of probable efficacy in groups of selected individuals. Although some RCTs limit inclusion criteria to a single category of diagnosis, many studies include individuals with different diagnoses such as schizoaffective disorder. In all RCTs, even in those recruiting people with a single DSM or ICD-10 diagnosis, there is considerable clinical heterogeneity.
Genome-wide association studies of large samples with schizophrenia demonstrate that this clinical heterogeneity reflects, in turn, complex biological heterogeneity. For example, genome-wide association studies suggest that around 1000 genetic variants of low penetrance and other individually rare genetic variants of higher penetrance, along with epistasis and epigenetic mechanisms, are thought to be responsible, probably with the biological and psychological effects of environmental factors, for the resultant complex clinical phenotype. A more stratified approach to clinical trials would help to identify those subgroups that seem to be the best responders to a particular intervention.
To date, however, there is little to suggest that stratification on the basis of clinical characteristics successfully helps to predict which drugs work best for which people. There is a pressing need for the development of biomarkers with clinical utility for mental health problems. Such measures could help to stratify clinical populations or provide better markers of efficacy in clinical trials, and would complement the current use of clinical outcome scales. Clinicians are also well aware that many people treated with antipsychotic medication develop significant adverse effects such as extrapyramidal symptoms or weight gain. Again, our ability to identify which people will develop which adverse effects is poorly developed, and might be assisted by using biomarkers to stratify populations.
The results of this review tend to indicate that as far as antipsychotic medication goes, current drugs are of limited efficacy in some people, and that most drugs cause adverse effects in most people. Although this is a rather downbeat conclusion, it should not be too surprising, given clinical experience and our knowledge of the pharmacology of the available antipsychotic medication. All currently available antipsychotic medications have the same putative mechanism of action — namely, dopaminergic antagonism with varying degrees of antagonism at other receptor sites. More efficacious antipsychotic medication awaits a better understanding of the biological pathogenesis of these conditions so that rational treatments can be developed.