In 77 studies that included 4,930 adolescents and 1,956 adults, two-thirds of patients entering substance abuse treatment programs reported at least one co-occurring mental health problem during the previous year. Attention deficit and conduct disorders were more common in young patients, anxiety and depression in older patients.
Source
Chan, Y.F., Dennis, M.L., and Funk, R.L. Prevalence and comorbidity of major internalizing and externalizing problems among adolescents and adults presenting to substance abuse treatment. Journal of Substance Abuse Treatment 34(1):14-24, 2008. [Abstract]