Severe statin adverse effects are rare but there is widespread reporting of less well-defined statin-related symptoms in the media, notably muscle pain and weakness that significantly affect statin users. These reports have been prompted by non-randomised, non-blinded observational studies but have not been confirmed in blinded randomised controlled trials (RCTs). A major limitation of observational studies is lack of blinding: patients taking a medication expect to experience adverse effects and therefore report high levels of symptoms vs. statin-free population. This phenomenon, the "nocebo" effect, leads to bias.