Attention Deficit Pays at Shire

"After 25 years and 35 studies, there is not a single straightforward experiment comparing typical unmedicated children with an ADHD diagnosis to typical controls," they concluded. "We are perplexed."

Nor have scientists fully studied the long-term effects of popular ADHD drugs.

Berkeley professor Nadine Lambert offers one of the more extensive -- and frightening -- reports available. Lambert set out to determine whether children who take ADHD drugs go on to abuse other stimulants, such as tobacco and cocaine, as adults. She found a troubling correlation.

"Childhood use of CNS (central nervous system) stimulant treatment is significantly and pervasively implicated in the uptake of regular smoking, in daily smoking in adulthood, as well as ... diagnoses of tobacco and cocaine dependence," she wrote.

But other experts, including Barkley, have criticized those results. They call Lambert's study flawed and highlight other research that contradicts her findings.

Andrea Arcona, a clinical psychologist and former colleague of LeFever's, sees a pressing need for more extensive ADHD research. She says that current "long-term" studies often stretch for just a few months even though they involve drugs that may be taken by children -- beginning as early as preschool -- who will go on to use them for decades.

"Does it really hurt when kids start taking a drug -- sometimes with other drugs -- and stay on it for that long?" she asked. "Nobody knows. The research is just not out there."