A study presented at the American Heart Association's scientific meetings has raised concerns about melatonin, one of Britain's most commonly prescribed sleep aids . The findings suggest that long-term users face a higher risk of heart failure. But the preliminary data demands careful scrutiny before the alarm is sounded. Melatonin has been prescribed in the UK for nearly two decades, with 2.5 million prescriptions issued in England last year alone . The drug is a synthetic version of the