BERKELEY, Calif., Aug. 15 (UPI) -- BERKELEY, Calif., Aug. 15 (UPI) -- As girls with attention-deficit hyperactivity disorder grow older they may internalize feelings of failure manifesting in self-injury, U.S. researchers say.

Lead author Stephen Hinshaw of the University of California, Berkeley, said girls with ADHD and their families often look forward to the likely decline in visible symptoms such as fidgety or disruptive behavior as they mature into young women.

However, as women enter adulthood, those with histories of ADHD are more prone to internalize their struggles and feelings of failure -- a development that could manifest itself in self-injury and even attempted suicide, Hinshaw said. 

The longitudinal study, which began when the girls were ages 6-12 in 1997, tracked a racially and socioeconomically diverse group of girls with ADHD in the San Francisco Bay Area. 

The study, published in the Journal of Consulting and Clinical Psychology, gauged the symptoms of two major ADHD subtypes: Those who entered the study with poor attention alone versus those who had a combination of inattention plus high rates of hyperactivity and impulsivity. 

More than half of the members of this subgroup were reported to have engaged in self-injurious behavior, and more than one-fifth had attempted suicide, Hinshaw said.

"Like boys with ADHD, girls continue to have problems with academic achievement and relationships, and need special services as they enter early adulthood," Hinshaw said in a statement. "Our findings of extremely high rates of cutting and other forms of self-injury, along with suicide attempts, show us that the long-term consequences of ADHD females are profound."