Taking illegal drugs and drinking too much alcohol are problems for some people with schizophrenia. When a person is using drugs, they are less likely to follow a treatment plan.
Most experts believe drugs and alcohol do not cause schizophrenia, but they may make antipsychotic medications less helpful. Also, drugs like marijuana make symptoms worse.
It is very common for people with schizophrenia to smoke cigarettes. However, smoking may make the medications less useful. It is hard for people to quit smoking because it might make their schizophrenia symptoms worse for a while. Doctors need to help any patient with schizophrenia who wants to quit smoking.
This answer from the National Institute of Mental Health has been reviewed and/or edited by Dr. William D. Knopf.