In a 10-year study by Biederman, et al. (2008), it was found that people with ADHD who took stimulant medication had neither a decreased or increased risk of substance abuse.

Biederman, J., Monuteaux, M.C., Spencer, T., Wilens, T.E., et al. (2008).  Stimulant therapy and risk for subsequent substance use disorders in male adults With ADHD: A naturalistic controlled 10-year follow-up study.  American Journal of Psychiatry, 165(5), 597-603.