People with drug problems often have co-occuring mental-health problems as well. A study of 419 people at a private rehabilitation centre in Johannesburg found that 57.1% of them had a mental-health problem. 155 had a mood disorder, 40 had an anxiety disorder, 39 had ADHD, 35 had an eating disorder, 8 had a conduct disorder and 5 had schizophrenia. ADHD was linked to cannabis-related disorders and polysubstance (more than one drug) dependence. Anxiety-related disorders were linked to alcohol abuse and mood disorders were linked to cocaine.
Fabricius, V., Langa, M. and Wilson, K. - An exploratory investigation of co-occuring substance-related and psychiatric disorders Journal of Substance Use April 2008, 13(2), 99-114