Therapeutic strategies must be chosen with an accurate and updated assessment of both expected benefits and potential risks to sustain the confidence of patients and guarantee safety. In a linked study (doi:10.1136/bmj.e3645), Azoulay and colleagues found that more than two years daily exposure to pioglitazone doubled the risk of bladder cancer.1 They also found an association between bladder cancer and both the dose and the duration of pioglitazone treatment.1 This nested case-control study benefits from the use of data from the large high quality General Practice Research Database. A new user design was used for the first time to study this particular risk. Strengths of the study also include adjustment for many confounders, the matching of case and controls on duration of follow-up, and comparison with the incidence of bladder cancer in patients exposed to rosiglitazone. These allowed the study’s authors to draw reliable conclusions with a minimal risk of indication bias due to severity of diabetes.

Much is known that places the current findings …