When psychiatrists say the words "dual diagnosis," they are almost always referring to a person who has a mental illness and a substance abuse problem. Drug and alcohol abuse are far more common among people with bipolar disorder than any other Axis I psychiatric disorder--and the lifetime prevalence is an astonishing 60 percent or more among those who have childhood- or adolescent-onset bipolar disorders. Drug and alcohol use also usually starts during the teenage years, sometimes even earlier.

Choice of drug may even be a diagnostic clue: up to 30 percent of cocaine addicts fit the criteria for bipolar disorder, as do a sizable portion of alcoholics and amphetamine users. It is not yet known whether these individuals abuse drugs as a result of their bipolar illness, or have bipolar-like symptoms as a result of their drug use. There is some pretty compelling evidence that the former, rather than the latter, is usually the case.

Substance abuse can complicate diagnosis and treatment. In the past, the conventional wisdom was that the alcoholic or drug addict had to be clean and sober before psychiatric treatment could succeed, but current clinical experience indicates that it's essential to treat the underlying bipolar disorder along with the substance abuse problem. In fact, mood stabilization may be a very necessary part of substance-abuse treatment for this population. Medication and therapy can greatly reduce the relapse rate.

Many people with bipolar disorder have other psychiatric or medical problems to contend with, a fact that can complicate their treatment and even contribute to mood swings. Several neurological and physical problems occur more often in people with bipolar disorder than in the general population. The list includes migraines, seizure disorders, ADHD, developmental delays, obsessive-compulsive disorder (OCD), Tourette syndrome, anxiety disorders, autism and other pervasive developmental disorders, autoimmune disorders, and gastrointestinal disorders. Many of these conditions have symptoms that can be mistaken for those of bipolar disorder.