CRD Summary: The authors concluded that the limited evidence available suggests that growth hormone may alter body composition, but has minimal effect on key athletic performance and may be associated with impaired exercise capacity and increased adverse events. The review was generally well-conducted and the conclusions are likely to be reliable.

CRD Commentary: The review objective and inclusion criteria were clear. Relevant sources were searched, although the restriction to English language studies may have meant that some studies were missed. In addition, there was little attempt to identify unpublished studies, thereby introducing the potential for publication bias. The authors reported no evidence of publication bias from inspection of the funnel plots; however, these plots were not presented in the report. Appropriate criteria were used to assess study validity and adequate information was provided about the primary studies. Steps were taken to minimise error and bias by having more than one reviewer independently extract the data and assess study validity, but the process used to select studies for inclusion was unclear. The decisions on which study outcomes to pool statistically appear appropriate. Suitable statistical methods were used for the meta-analysis and to assess heterogeneity and publication bias. The review was generally well-conducted and the conclusions are likely to be reliable.