Dual Disorder in psychiatry refers to the presence of two distinct illnesses occurring simultaneously. Although the term appears to be rather generic, it generally is used to refer to the presence of a substance use disorder such as alcoholism occurring simultaneously with another primary psychiatric illness such as major depression.

Substance use disorders often cause phenomena that look very much like other psychiatric disease. There are diagnoses possible for substance-induced mood disorders and substance-induced anxiety disorders, for example. For this reason, the DSM-IV advises that diagnoses of primary psychiatric disorders not be made in the absence of sobriety (of duration sufficient to allow for any substance-induced symptoms to dissipate).