Attention Deficit Hyperactivity Disorder (ADHD) is one of the most commonly diagnosed childhood disorders and can continue through adolescence into adulthood. Diagnoses exploded in the 1990s and now it is found in about 5% of children, but such diagnosis is based on clinical judgment rather than objective diagnostic markers. Symptoms include difficulty focusing attention and remaining "on task", impulsive behavior and extreme hyperactivity but some diagnoses have been made even when those behaviors were mild, so chemical interventions should be cautiously - but they are not.

Methylphenidate, more commonly known by its brand names - Ritalin®, Concerta®, Medikinet®, and Equasym®, amongst others - has been used to treat "hyperactivity" and then ADD and ADHD for over 50 years. A team of Cochrane researchers evaluated and summarized the findings from all of the available randomized trials of this widely used drug and found evidence of increased sleeplessness and loss of appetite leads in use of methylphenidate.

This new Cochrane Review includes data from 185 randomized controlled trials involving more than 12,000 children or adolescents. The studies were conducted mainly in the US, Canada, and Europe, included males and females from ages 3-18, and all compared methylphenidate with either a dummy pill or no intervention.

When researchers combined data from identified trials, they found that methylphenidate led to modest improvements in ADHD symptoms, general behavior, and quality of life. Analysis of adverse effects showed that children were more likely to experience sleep problems and loss of appetite while taking methylphenidate. However, the researchers' confidence in all results was very low: it was apparent from assessing the included trials that it would have been possible for people involved in the trials to have been aware of which treatment the children were taking. In addition, the reporting of results was not complete in many of the trials, and for some analyses there was variation among trial results. 

Based upon this information, the researchers urge clinicians to be cautious in prescribing methylphenidate, and to weigh up the benefits and risks more carefully. 

Co-author Camilla Groth MD said, "This review shows very limited quality evidence for the effects of methylphenidate on children and adolescents with ADHD. Some might benefit, but we still don't know which patients will do so. Clinicians prescribing methylphenidate must take account of the poor quality of the evidence, monitor treatment carefully, and weigh up the benefits and adverse effects."

An abridged version of the Cochrane Review will appear in the BMJ later this week.