Comorbidity: Substance Use Disorders and Other Mental Illnesses

Substance use disorders change the brain in fundamental ways, changing a person’s normal needs and desires and replacing them with new priorities connected with seeking and using the substance. This results in compulsive behaviors that weaken the ability to control impulses, despite the negative consequences, and are similar to hallmarks of other mental illnesses.

https://www.drugabuse.gov/publications/drugfacts/comorbidity-substance-use-disorders-other-mental-illnesses