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The link between schizophrenia and substance abuse illuminated

“A 29-year-old Caucasian man was brought to the emergency department by the police after he was found wandering barefoot through the snow on Main Street. The police had been called after passers-by reported that the man seemed intoxicated and was acting strangely. When an officer approached the man, he became belligerent and agitated and angrily exclaimed that they had no reason to question him. Using some force, the police brought him to the emergency department. The psychiatrist who interviewed him noted a strong smell of alcohol and signs of psychosis; the man demonstrated a clear thought disorder, and he appeared to be responding to internal voices.” This common clinical scenario illustrates the strong link between schizophrenia and co-occurring substance disorders.

Theories attempt to explain why

Studies have suggested that approximately 50 percent of individuals who are diagnosed with schizophrenia have a co-occurring substance abuse disorder — specifically alcohol and/or cannabis abuse. “Rates of cannabis use disorder as high as 53 percent have been reported in some studies of patients with first-episode schizophrenic psychosis, and cannabis use has been associated with an earlier age at onset of schizophrenia, an elevated risk of developing psychosis, and a higher relapse rate after remission of acute psychotic symptoms in the first episode.”

Many plausible theories attempt to explain why there is a link between substance use disorder and schizophrenia: The neurobiology of schizophrenia places individuals more at risk with environmental stressors; individuals with schizophrenia are more at risk for substance use disorder because they tend to have poor cognitive, social, vocational and educational functioning; and individuals with schizophrenia use substances to self-medicate.

The role of the dopamine reward system

Reward circuitry dysfunction has also been implicated as a cause for the link between schizophrenia and substance abuse. The anatomical areas in the brain that are involved in schizophrenia are thought to also be involved in the dopamine reward system, which is the prominent system in the brain that is involved with cravings and substance abuse. These patients are thought to not have normal levels of dopamine and, therefore, this pathway is not properly stimulated by normal external environmental rewards, leading individuals to use drugs to hijack this dopamine reward system.

Unlike alcohol, marijuana has its own natural receptors in the brain, known as cannabinoid receptors, and when marijuana is bound to these receptors, it disrupts brain signals across the hippocampus and the prefrontal cortex, which are important areas responsible for concentration and memory. These areas in the brain are in disarray in patients with schizophrenia, leading to a defect in executive functioning. In addition, when THC is given intravenously to patients without schizophrenia, it has been shown to illicit psychosis in these patients, strengthening the link between marijuana and schizophrenia.

Treating co-occurring disorders

Marijuana abuse is common among sufferers of schizophrenia and recent studies have shown that the psychoactive ingredient of marijuana can induce some symptoms of schizophrenia in healthy volunteers. These findings are therefore important for our understanding of psychiatric diseases, which may arise as a consequence of ‘disorchestrated brains’ and could be treated by re-tuning brain activity.”

It is important for clinicians to keep in mind that a substance use disorder may be on the forefront with anyone who has been diagnosed with schizophrenia and treating co-occurring disorders is much different than treating a mental health disorder alone. If the substance abuse issue is mismanaged then it can easily derail the patient’s schizophrenia by destabilizing the illness and impeding treatment.

Sovereign Health of Texas is a leading behavioral health treatment provider that uses a holistic approach to treat individuals who struggle with addiction and dual-diagnosis disorders like schizophrenia and substance abuse. Our facility is equipped to serve both English- and Spanish-speaking patients. For more information, please call our 24/7 helpline.

About the author

Kristen Fuller, M.D., is a senior staff writer at the Sovereign Health Group and enjoys writing about evidence-based topics in the cutting-edge world of medicine. She is a physician and author, who also teaches, practices medicine in the urgent care setting and contributes to medicine board education. She is also an outdoor and dog enthusiast. For more information and other inquiries about this article, contact the author at

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