Nicotine, alcohol and other drugs of abuse target dopaminergic, glutamatergic, and GABAergic transmission, which are also involved in the pathophysiology of severe mental illness. Specifically, nicotine can increase the metabolism of anti-psychotics by activation of the cytochrome P450 enzymes 33, and is thus hypothesized to help reduce side effects of individuals taking antipsychotics. Conversely, exposure to substances increases risk of severe mental illness: marijuana use at age 16 is associated with psychosis at age 19 34, and smoking precedes the onset of symptoms of mental illness 35,36. Additionally, substance use leads to higher rates of psychiatric emergencies and hospitalizations 37. This highlights the importance of understanding the biological connection between substance use and severe mental illness.
