Many people living with mental illness are also living with substance abuse disorders and other medical conditions. The need for integrated health care is even more critical for individuals with these co-occurring, or dual-diagnosis, conditions.
The mental health and substance abuse treatment systems historically have had different cultures and expectations, and didn't get too involved with each other. Now it is finally clear that in order to appropriately treat individuals, care should be integrated. The system of care for people with dual- diagnosis is learning to get more integrated and more creative while improving the ability of mental health professionals to screen and intervene with substance abuse problems and vice versa. Visit Hearts & Minds section on co-occurring disorders for more information on this topic.
There are many great resources available to help you understand this complex issue. A great place for information on this effort is U.S. Substance Abuse and Mental Health Services Administration (SAMHSA) Web site on Co-Occurring Center for Excellence.