A study has found that more children taking drugs to treat attention-deficit hyperactivity disorder died suddenly from cardiac complications or unknown causes than in car accidents, but US regulators insist that parents should not use the findings as a basis for stopping treatment.

The study, which was jointly funded by the Food and Drug Administration and the National Institute of Mental Health and is published in the American Journal of Psychiatry, looked at the use of stimulant medication in 564 healthy children across the US who died suddenly and 564 children who lost their lives in car accidents.

It was discovered that in the sudden deaths group 10 children were on ADHD medication, such as Novartis’ Ritalin (methylphenidate) and Shire’s Adderall XR (mixed amphetamine salts), compared to just two of those who died in a car crash, leading the researchers to conclude that there could be a link between stimulant medication for ADHD and sudden death.

However, in a communication posted on its website the FDA stresses that because the study has several limitations - such as the higher likelihood of a post mortem in children dieing suddenly than those dieing in car crashes - which could skew results, it cannot conclude that the data affect the overall benefit-to-risk profile of stimulant medicines.

The safety profile of ADHD drugs has long been in question. In February 2007 the FDA ordered manufacturers of all ADHD medicines to develop Patient Medication Guides warning over the risk of cardiovascular events and psychiatric side effects associated with these products.

CV risks already flagged
The move was prompted by a review of serious cardiovascular adverse events in patients taking usual doses of ADHD products, which revealed a number of sudden deaths in patients with underlying serious heart problems, stroke and heart attacks in adults with risk factors, and a small increased chance of psychiatric problems such as hearing voices and mania.

And now the FDA is currently undertaking a comprehensive review of this latest research and other epidemiological studies assessing the safety of stimulant medications in children. In addition, in partnership with the Agency for Healthcare Research and Quality the agency is sponsoring a large epidemiological study that will provide further information about the potential risks of these drugs, and so it notes that its advice could be updated as new findings become available.