Addiction and mental illness are identified as separate and distinct issues that can—and often do—occur together. Effective treatment for co-occurring disorders depends on an accurate diagnosis, which can be a highly complex and somewhat subjective process. Some key considerations related to the prevalence, diagnosis, and treatment of co-occurring disorders are discussed below. What is a co-occurring disorder? Co-occurring disorder, also known as "dual diagnosis" or "comorbid condition," refers to the coexistence of a substance use disorder—alcohol or other drug abuse or dependence—and a mental health disorder. Mental health disorders that commonly occur with addiction include mood disorders, such as depression or bipolar disorder; eating disorders; and anxiety disorders, including post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder. Are people with addiction at greater risk of having a co-occurring mental health disorder? As reported in Hazelden's Research Update on "Addiction and Mental Illness," the prevalence of substance use disorders in the general population is about 16 percent and nearly doubles to 29 percent for people with mental health disorders. Additionally, the publication provides the following facts and figures on the prevalence of co-occurring disorders: Depression. Depression is often found at high levels among alcoholics and addicts seeking substance dependency treatment. As many as 80 percent of alcoholics experience depressive symptoms at some time in their lives, and 30 percent meet diagnostic criteria for major depression. PTSD. There is a strong correlation between substance use disorders and PTSD, with as many as one-third of patients meeting criteria for PTSD when they enter treatment for their alcohol/drug problems. Anxiety disorders. Rates of other anxiety disorders, such as agoraphobia, panic disorder, social phobias, and general anxiety disorder, are high in treatment populations, ranging from 10 to 60 percent. Eating disorders. Most studies find that between 15 and 32 percent of women with alcohol/drug disorders meet diagnostic criteria for an eating disorder at some time in their lives. Why do these disorders occur together so frequently? While answers about co-occurrence aren't conclusive, there are many theories. The Dartmouth Psychiatric Research Center puts forth several theories, including the following: Self-medication. People use alcohol or other drugs to "self-medicate" against disturbing symptoms of mental illness. Early onset. Certain drugs of abuse (e.g., methamphetamine, cocaine, alcohol) may precipitate an earlier onset of mental illness in certain vulnerable individuals. Genetic and environmental. Genetic predisposition or environmental factors (poverty, social isolation, or lack of structure, for example) may cause both substance use problems and mental illness. Susceptibility. People with mental illnesses may be more susceptible to the harmful effects of alcohol and other drugs. Why is it difficult to diagnose co-occurring disorders? Psychiatry is a complex field with regard to diagnostic assessment. Blood tests and lab procedures don't provide conclusive diagnoses for psychiatric illness. Co-occurring disorders can be especially problematic to diagnose because the presence of one disorder can interfere with diagnosis of the other. For example, a person with alcohol or other drug dependence is likely to manifest problems with depression or anxiety. Likewise, a person seeking medical care for depression or anxiety may downplay or deny his or her alcohol use. Conducting a comprehensive evaluation is of paramount importance because effective treatment of co-occurring disorders is diagnosis driven. What type of treatment is recommended for co-occurring disorders? An integrated treatment approach is key, with a focus on stabilizing symptoms of the co-occurring mental health disorder while providing the patient with a foundation for recovery from addiction.