For decades, experts have questioned the increase in A.D.H.D. diagnoses among children and adolescents. The rates far outstrip estimated prevalence of the disorder, and the first-line treatment is almost always a prescription for stimulant medication.

The new study suggests that the increase has happened among adults, too.

Recent changes in diagnostic guidelines have extended the criteria to adults who have experienced inattentiveness and restlessness since childhood. Psychiatrists generally accept longstanding A.D.H.D. as a valid, treatable disorder in adults.

But many also acknowledge that these drugs have wide appeal as performance-enhancers: among students as study aids, and among adults seeking an edge in their work.

Yet prevalence studies, using strict criteria, estimate that around 3 percent of adult women overall have A.D.H.D., well under the 5 percent and higher rates recorded in some age groups by the C.D.C.

The new study is also relevant to more recently proposed diagnosis: adult-onset A.D.H.D., in which symptoms emerge out of blue, well after adolescence. Experts fiercely debate whether this diagnosis is valid, and a recent study concluded that the disorder did not exist.

“If adult symptoms are being reported by patients, it shouldn’t necessarily be immediately classified as A.D.H.D.,” said Margaret Sibley, an associate professor of psychiatry and behavioral health at Florida International University, the lead author of that study.

“A more careful evaluation often finds that there’s something else causing the problems, like depression, or drug use — which is what we found.”