CRD Summary: This review assessed the effect size of lithium in short-term efficacy studies of moderate to severe manic episodes and concluded that lithium was effective. The reliability of the conclusion was unclear given the limitations of the review in terms of the literature search, reporting and possible methodological weaknesses.

CRD Commentary: The review addressed a clear question. The search was limited to two databases, but efforts were made to find unpublished studies by searching the registration file submissions to the Medicines Evaluation Board. The inclusion and exclusion criteria were clear with the exception of outcome measures. It was not reported how study selection and data extraction were performed, so reviewer bias and error might have been introduced. The inclusion criteria stipulated placebo controlled randomized trials, but it was not reported whether or not a formal assessment of validity was performed, therefore, the potential impact of methodological flaws of the studies upon the reliability of the findings could not be assessed. Appropriate methods were used to pool the results and to investigate statistical heterogeneity. The reliability of the authors' conclusion was unclear given the limitations of the review in terms of literature search, reporting and possible methodological weaknesses of the review.