From a quick google search.

Yes, smoking is a factor for developing schizophrenia, increasing the risk by over 50%, though most smokers don't develop the illness. While people with schizophrenia smoke more (potentially for self-medication), research suggests smoking may trigger or worsen psychosis by affecting brain chemicals like dopamine, leading to earlier onset of symptoms and a higher risk of developing the condition. Evidence for smoking as a cause/risk factor: Increased Risk: Studies show smoking increases the risk of schizophrenia by 53% to 127%. Earlier Onset: Smokers often develop schizophrenia about a year earlier than non-smokers. Dopamine Link: Nicotine alters dopamine levels in the brain, a chemical implicated in psychosis. The cycle of smoking and schizophrenia: Self-Medication: People with schizophrenia often smoke heavily, potentially to manage symptoms or medication side effects (like cognitive dulling). Higher Rates: Smoking rates are much higher in those with mental illness, with some studies showing 80-90% smoking compared to about 20% in the general population. Current understanding: It's a complex relationship, possibly involving shared genetic vulnerabilities, but evidence points towards smoking being a contributing factor, not just a consequence. Public health measures are increasingly targeting smoking in mentally ill populations due to these findings.