INTRODUCTION For patients, clinicians, and other decision makers to make informed, balanced decisions, they need appropriate information on both the intended benefits and undesirable consequences of an intervention. However, currently there is an absence of sufficient evidence-based information on the frequency or magnitude of adverse effects. Long lists of potential adverse effects may be all that can be found, with little or no information available as to the magnitude of these effects or of the probability of their occurrence [1-3]. One potential solution to this problem would be to incorporate data on adverse effects into systematic reviews. Systematic reviews are one of the most powerful and reliable tools to estimate the magnitude of effects and the probability of their occurrence [4-10].