BAKERSFIELD, Calif. -- In 1999, a landmark study on children with attention-deficit/hyperactivity disorder -- also known as ADHD -- found that a combination of medication and behavioral therapy worked best for treatment.

Now, long-term follow-up of these children has provided new information on what ADHD is like as kids get older. Results showed only about half of kids improved right after starting drug treatment, while a third improved more gradually.

More than one in 10 children responded well at first, but the medication's benefits decreased over time. After about three years, kids taking ADHD drugs were no better off than those in behavioral therapy.

The study confirmed that stimulant medications such as Adderall and Ritalin slow children's growth by about 3/4ths of an inch. Experts said it's important to get kids treated early and then to take periodic breaks from the drugs to see if children still need them.

And doctors pointed out that treatment of any kind is not a cure-all -- children with ADHD were still about three times as likely to have behavioral problems and twice as likely to abuse drugs or alcohol.