A rational use of drugs depends on the balance of potential benefits and adverse effects applied to the individual patient [1]. A problem in achieving such a balance derives from the different sources of information that need to be integrated. Guidelines tend to place emphasis on systematic reviews and meta-analyses of randomized controlled trials that are uniquely geared to detecting benefits [1]. Observational studies tend to be considered to have less validity, despite evidence to call such a view into question [2]. The appraisal of adverse effects relies primarily on observational studies and data from routine clinical practice and may not emerge from randomized controlled trials, unless these effects occur early in treatment and are specifically investigated [1].
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