Diabetes drug 'doubles bladder cancer risk'
Academics found pioglitazone, taken by some 20,000 people and used to control blood sugar levels, increased the risk, but a comparable drug called rosiglitazone did not.
Writing online in the British Medical Journal, the researchers, from the Jewish General Hospital in Montreal, Canada, said their results "provide evidence that pioglitazone is associated with an increased risk of bladder".
They noted that in absolute terms, the risk of getting bladder cancer was still small in those taking pioglitazone.
The general rate of bladder cancer in British over 65s is 73 per 100,000 person years.
Both drugs are already known to increase the risk of heart failure.