CRD Summary: This review found no evidence of a beneficial effect of nimodipine over placebo in patients with traumatic subarachnoid haemorrhage following head injury. The authors' conclusions are in line with the evidence presented, but methodological weaknesses in the review suggest that the conclusions should be treated with caution.

CRD Commentary: This review addressed a clear question and had clear inclusion criteria. The authors searched two databases for studies in a restricted range of languages, which means that relevant studies could have been missed. Publication bias was not assessed and the authors noted that one included trial was not fully published, possibly because the results were disappointing; this suggests that publication bias could be an issue for this review. Validity was assessed using a standard scale. Validity was assessed by only one reviewer and the methods used to select studies and extract the data were not reported; this makes it difficult to assess the risk of reviewer error and bias affecting the review process.

Limited details of the included studies were reported, which makes it difficult to assess similarities and differences between them. The studies were pooled by meta-analysis for the primary outcome. Significant statistical heterogeneity was present, suggesting that the decision to pool the studies might not have been appropriate. The possible sources of heterogeneity were not explored. The authors' conclusions are in line with the evidence presented, but the issues identified above suggest that they should be treated with caution.