I will open this post with the bottom line. No one has the definitive answer to this question. Yet. But interesting information can be found in a study published last month in The American Journal of Psychiatry. This study suggests that ADHD in adults does not start in childhood, but is a different disease process. It also suggests that most children with ADHD do not carry that process forward into adulthood.
The study followed over 1,000 individuals born in New Zealand in 1972 and 1973. They were assessed for ADHD regularly throughout childhood, and periodically in adulthood. A remarkable 95% of the participants completed the study. 6% of study participants were diagnosed with ADHD in childhood. At age 38, 3% of the participants carried the diagnosis of ADHD. Notably, only 10% of the adults with ADHD had ADHD which started in childhood. And only 5% of individuals with childhood ADHD still carried that diagnosis at age 38.
Childhood ADHD and adult ADHD also seemed to be different illnesses. Those with childhood ADHD were predominantly male (79%), had neurocognitive deficits, positive genetic risk profiles, and significant problems with conduct disorder. ADHD in adults was equally distributed between men and women, and these adult showed no genetic risk for ADHD, nor did they have the neurocognitive problems seen in childhood ADHD.
More study needs to be done on this issue, but it appears childhood and adult ADHD may be two different illnesses. The clinical implications are potentially significant. For children with ADHD, stimulants can be profoundly life-improving. But what often happens is that once a child is started on stimulants, those medications are continued well into adulthood. The New Zealand study raises legitimate questions about whether this is an appropriate practice. This is a difficult question, since most patients who have been on stimulants for years will be very reluctant to consider stopping them. However, given the potential serious side effects of long-term stimulant use, it is medically reasonable to consider the risks and benefits of continuing this class of medications long into adulthood. For primary care clinicians, this issue can be very complicated. Enlisting the wisdom and experience of a behavioral medicine specialist can be very helpful as our childhood ADHD patients grow into adulthood.
Richard Fleming, MD