Attention deficit hyperactivity disorder drugs do not increase the risk of strokes, heart attacks or sudden cardiac death, according to a major study.

The study, the data from which has been published in the New England Journal of Medicine, involved over 1.2 million children and young adults (aged 2-24 years) who were taking ADHD drugs. The results revealed that there were 81 serious cardiovascular events, or 3.1 per 100,000 person-years, including 33 sudden cardiac deaths, nine acute myocardial infarctions and 39 strokes.

Researchers said that youngsters receiving ADHD drugs were no more likely to suffer a serious cardiovascular event than were non- and former-users of the treatments.

The US Food and Drug Administration also noted that there were just seven serious cardiovascular events in current users (four strokes and three sudden cardiac deaths). This equates to a rate of 1.87 events per 100,000 person-years, "suggesting a low absolute risk".

However, this also limited the ability to make statistical comparisons to rates in patients not using ADHD drugs, the agency said, noting that the results were not consistent with the seven-fold increase in sudden death reported in a previous case-control study. Still, the FDA added that "a small to modest increase in risk cannot be excluded".

This is the first of three studies that were sponsored by the FDA and the Agency for Healthcare Research and Quality after reports of serious cardiovascular adverse events.