Substance abuse is endemic in the general population and there is no reason why individuals with schizophrenia should be exempt. Therefore, many individual with schizophrenia who are abusing alcohol and street drugs would also be doing so if they never had schizophrenia.

• Make them 'feel good'
• Provide social network and something to do for individuals who are often isolated.
• 'Self medicating' alcohol, marijuana, and cocaine : decreased anxiety, decreased depression, and increased energy.
• Possible genetic connection between predisposition to schizophrenia and a predisposition to alcoholism.