In what ways are schizophrenia and bipolar disorder related to substance abuse? why?

Not always related: Schizophrenia, bipolar disorder and substance use are not always related. Patients with these illnesses will sometimes self medicate with substances to help them cope with their symptoms. Patients with no prior mental illness will find themselves with schizophrenia-like symptoms due to drug abuse. There are patients with these illnesses that do not use drugs. Tobacco use though is very common.

See below: Schizophrenia not often associated but bipolar is. During the manic phase, people are more impulsive and also are less concerned about the consequences of their actions. During the depressed phase they look to drugs too relieve symptoms of depression.

Research has shown..: Schizophrenia seems to be linked to cigarette smoking substance abuse because the nicotine affects the nerves in the auditory processing centers of the brain and may reduce the feelings of hearing voices inside the head.