Medications to treat attention deficit hyperactivity disorder (ADHD) do not increase children’s risk of substance abuse later in life if they start taking them early and for a long period, a new study suggests.

The odds of any substance use were more than two times as likely among those who started taking ADHD medications at age 15 or older, and took them for two years or less, compared with those who started treatment at age 9 or younger, and took the drugs for six years or more, HealthDay reports.

The findings appear in the Journal of the American Academy of Child and Adolescent Psychiatry.