Randomised controlled trials (RCTs) of drug interventions for schizophrenia that also used ginkgo as an adjunct therapy were eligible for inclusion. Trials were excluded if they used electroconvulsive therapy and transcranial magnetic stimulation, or rapid tranquilisation as part of the intervention. Trauls were also excluded if duration of treatment was less than two weeks. The primary outcome was response to treatment monitored using a standardised symptom rating scale.
All the included trials used a standardised extract of ginkgo in the form of EGb (a compound derived from dried ginkgo leaves); dosage ranged from 120 to 360mg/day. Antipsychotic drugs also included were chlorpromazine, clozapine, haloperidol, olanzapine or combined regimens. Most included trials were compared with placebo. Total symptoms were measured using either the Scale for the Assessment of Positive symptoms (SAPS) or the Brief Psychiatric Rating scale (BPRS). Negative symptoms were measured using the Scale for the Assessment of Negative Symptoms (SANS).
Diagnosis of schizophrenia varied between trials, but all participants were considered to have chronic schizophrenia. The age of participants ranged from 28 years to 46 years; the proportion of men ranged from 50 to 82%. Most trials reported illness duration of between six and eleven years, but one trial reported illness duration of patients of 21 years. Trial duration ranged from eight to 16 weeks. Most trials were conducted in China, with the remainder conducted in Turkey.
Two reviewers independently selected studies for inclusion.