Why do mental illness and drug addiction so often go together? New research reveals that this type of dual diagnosis may stem from a common cause: developmental changes in the amygdala, a walnut-shaped part of the brain linked to fear, anxiety and other emotions.
Dual diagnosis is common yet difficult to treat. Addiction of all types -- to nicotine, alcohol and drugs -- is often found in people with a wide variety of mental illnesses, including anxiety disorders, unipolar and bipolar depression, schizophrenia, and borderline and other personality disorders. Lead author Andrew Chambers, MD, cites clinical reports that at least half the people who seek help with addiction or mental-health treatment have co-occurring disorders. Epidemiological data says that from two to five of every 10 anxious or depressed people, and from four to eight of every 10 people with schizophrenia, bipolar disorder, or antisocial personality, also have some type of addiction.
"Brain conditions may alter addiction vulnerability independently of drug history," says Chambers. He and his colleagues concluded that someone's greater vulnerability to addiction, rather than a given drug's ability to alter the symptoms of mental illness for better or worse (usually worse), more fully explains the high rates of dual diagnosis.
For these reasons, and given the lab evidence and the fact that dual diagnosis patients do less well on psychiatric medication than other patients, Chambers wondered whether the underlying problems in the brain -- what he calls "neural inflexibility" -- make it harder for these people to respond.
To improve the effectiveness of treatments for dual diagnosis, Chambers would like to see educators, counselors, physicians, and scientific researchers integrate insights into both mental health and addiction. Funding the simultaneous treatment of both disorders would also help, he observes, given that "dual-diagnosis cases are the mainstream among these patients, probably because addiction and mental illness are strongly linked by neurobiology."