Weed and Schizophrenia: an increasingly clear correlation

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Substance abuse, and marijuana use specifically, is rising around the world. In the United States alone, 13% of Americans reported starting or increasing their use of substances to cope with COVID-19 related stress or emotions (Centers for Disease Control and Prevention, 2020). 

Although it is well known that early drug abuse correlates with a variety of problems later in life, many do not have a clear idea of the link between the drugs they are so frequently using and several psychological and psychiatric disorders, including specifically schizophrenia and an increased risk of anxiety and depression. 

Marijuana, also known as cannabis, weed or pot, is the dried flowers, leaves, stems and seeds of the cannabis plant. This drug is impairing, or mind altering and can cause a ‘high’. Today, marijuana can be used in several ways, including being smoked in joints or blunts (like cigarettes), vaped using electronic devices, or mixed and infused in foods and drinks. The drug produces different effects depending on the amount taken, the frequency of usage, and the method in which it is used, and like most other drugs can create dependency. 

It is important to distinguish that marijuana and cannabis are not interchangeable terms, as cannabis refers to any product derived from the plant cannabis sativa while marijuana refers to products derived from specific parts of the plant containing delta-9-tetrahydrocannabinol (THC)

Today, more than 40 countries around the world have legalized cannabis for usage in medical treatments, as it has proven useful for a variety of reasons. Marijuana is commonly used in treatments for diseases including rare forms of epilepsy, nausea and vomiting experienced by cancer patients during chemotherapy, and appetite or weight loss associated with HIV/AIDS. Unfortunately, the helpful aspects of marijuana often obscure the serious repercussions that the usage of this drug can have on mental health, specifically on the increased chance of developing schizophrenia. 

Schizophrenia is defined by the Cleveland Clinic as a “spectrum of disorders that all involve a disconnection from reality, including hallucinations and delusions”. Although there is no single cause of the condition, genetics, viruses, poor nutrition, and issues with key brain chemicals may all play a part in the onset. There are about 2.77 million new schizophrenia diagnoses each year, worldwide, and recent research is showing that “smoking high quantities of marijuana every day could increase the chance of developing this disorder by nearly 5 times compared to people who have never used marijuana” (NIDA, 2020). 

A study conducted in Denmark and covered by CNN reporter Katie Hunt found that schizophrenia cases linked with incorrect usage of marijuana have increased over the past 25 years: “in 1995, 2% of schizophrenia diagnoses in the country were associated with cannabis use disorder. In 2000, it increased to around 4%. Since 2010 that figure increased to 8%” (Katie Hunt, CNN, 2021). Although the usage of marijuana is not singularly responsible for the onset of schizophrenia, a correlation is becoming increasingly clear. 

A 2020 systematic review looked at 96 studies and found that cannabis use can alter the typical age of onset for schizophrenic symptoms, can induce psychosis and eventually lead to clinical schizophrenia, frequent use can double the chances of developing the disorder, and it may interact with preexisting factors to increase schizophrenia risk (JM. Grohol and H. Gillette, 2020). Using marijuana with a pre-existing schizophrenia diagnosis may also worsen symptoms, and psychotic episodes may increase along with time spent at the hospital. Unfortunately, it is unrealistic to expect all young adults to stop using marijuana and cannabis, but it is fair to hope that the usage will decrease as the research relating this practice to schizophrenia becomes increasingly clear. It is best to encourage the younger population to withhold from these practices until later in life, and if a dependence is present at a young age, to engage in behavioral therapies to subdue it. 

By Carlotta Menozzi



Abramson, A. (2021, March 1). Substance Use during the Pandemic. American Psychological Association. https://www.apa.org/monitor/2021/03/substance-use-pandemic

CDC. (2021, September 10). What We Know About Marijuana. http://Www.cdc.gov. https://www.cdc.gov/marijuana/what-we-know.html

Cleveland Clinic. (2018). Schizophrenia | Cleveland Clinic. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/4568-schizophrenia

CNN, K. H. (2021, July 26). Schizophrenia linked to marijuana use disorder is on the rise, study finds. CNN. https://www.cnn.com/2021/07/22/health/marijuana-schizophrenia-study-wellness/index.html

Grohol, J. M., & Gillette, H. (2022, April 29). Cannabis and Schizophrenia: What’s the Link? Psych Central. https://psychcentral.com/schizophrenia/link-between-cannabis-and-schizophrenia

MacIver, B. (2017, June 29). Cannabis Legalization World Map. Cannabis Business Times; Cannabis Business Times. https://www.cannabisbusinesstimes.com/article/cannabis-legalization-world-map/

National Center for Complementary and Integrative Health. (2019, November). Cannabis (Marijuana) and Cannabinoids: What You Need to Know. NCCIH. https://www.nccih.nih.gov/health/cannabis-marijuana-and-cannabinoids-what-you-need-to-know

National Institute on Drug Abuse. (2020, July). Is marijuana addictive? National Institute on Drug Abuse. https://nida.nih.gov/publications/research-reports/marijuana/marijuana-addictive

Seed, S. (2018, October 31). Schizophrenia and Marijuana: Trigger or Treatment? WebMD; WebMD. https://www.webmd.com/schizophrenia/schizophrenia-marijuana-link


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