A major shift in the way researchers and clinicians look at attention deficit hyperactivity disorder (ADHD) may be on the horizon, according to two new studies that each tracked thousands of people for almost 20 years after birth. One group was in the United Kingdom while the other was in Brazil, but the findings from both, published in JAMA Psychiatry, were remarkably similar in two ways: Both found that a significant proportion of adults with ADHD did not have the condition as children, and the majority of those adults were women.