Comorbidity is the rule rather than the exception for substance use disorders, especially when they involve drugs other than alcohol. A common reaction of physicians to comorbidity is to attribute the substance use of addicted people to "self-medicating" with drugs of abuse. When an individual uses an abused drug nonmedically, he or she is seeking brain reward, not treatment. To confuse this drug-using behavior with treatment is to misunderstand addictive behavior and to encourage a false sense that the primary clinical task is to lower the dysphoria associated with the comorbid condition in order to stop the nonmedical drug use. Even the most effective treatment of comorbid disorders is unlikely to halt the addictive drug use. The best way to handle comorbidity (e.g., depression and alcoholism) is to consider each of the comorbid conditions to be a separate and serious illness deserving of effective and specific treatment and not to consider one to be a "symptom" of the other. While it is desirable to treat all comorbid conditions using the best practices for the treatment of that condition it is not reasonable to assume that one of the comorbid disorders is secondary to the other and therefore that treatment of the "secondary" disorder is irrelevant or unnecessary.