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Alcohol & Other Drugs

Cannabis (Marijuana) and Psychosis

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Author: BC Schizophrenia Society


People at risk for schizophrenia who use cannabis get their first symptoms at a younger age, and people with a mental illness who use cannabis have a harder time in their recovery.

Can using marijuana trigger psychotic illnesses like schizophrenia?

Probably, yes. Psychotic illnesses are mental illnesses that have symptoms of hallucinations, delusions and paranoia. These symptoms together are called “psychosis”. Schizophrenia is the best known psychotic illness. Some other psychotic illnesses are schizoaffective disorder and depression with psychotic symptoms. A large number of scientific studies agree that people who use cannabis (marijuana) before the age of 25 get illnesses like schizophrenia younger than they would have otherwise. They also agree that the more cannabis a person uses, the younger they will be when they start to be ill.


What does marijuana do to the brain?

On brain scans, the hippocampus (a part of the brain) shows up smaller for people who use cannabis heavily and for a long time compared to people who do not use cannabis. These people also have a harder time learning and remembering new information.


What causes schizophrenia?

Schizophrenia is a brain illness that is caused by things you are born with and things that happen to your brain during your life. People who have a family history of mental illness have a larger risk of developing schizophrenia. If you have a parent, grandparent, brother or sister with schizophrenia, depression, alcholism or substance use problems, it is a good idea to avoid using cannabis. It is also a good idea for everyone to take good care of their brain with healthy food, exercise and good sleep habits.


If I have a mental illness with psychotic symptoms, does using marijuana make it harder for me to recover?

Probably. People with a mental illness like schizophrenia seem to have a slower, harder time recovering if they are using cannabis. They also seem to have more relapses, and need to be in hospital more for their illnesses. If you use cannabis and have a mental illness, it is important to let your physician or clinician know. Knowing about your cannabis use will help them make better decisions about your treatment. For some people with schizophrenia or psychosis who use cannabis, stopping or using less will help them think more clearly and have an easier time working and living.


Ways others have found useful to help them quit

  • Find other things that give you what the drug used to provide. For example, if you use cannabis when bored or lonely, plan other activities to deal with boredom or loneliness.

  • Plan ahead of time what to say to turn down cannabis if it is offered to you.

  • Avoid situations or activities where you know you will feel tempted to use.

  • Spend time with friends who don’t use cannabis or other street drugs.

  • Visit with friends who do use cannabis in places where it will not be possible to use it.


Getting help when you have a mental illness and also use cannabis regularly

As someone with a mental illness, it is important to always consult with your physician before changing medication dosage or going off medication. Drug and alcohol services or support groups that suggest or require going off your prescribed medication are not a good fit for you. Ask your physician or mental health service provider about “dual diagnosis” programs in your area. These are programs that understand how to work with people who have both a mental illness and use substances. Not all alcohol and drug treatment services know about the needs of people with mental illness.



About the author

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The BC Schizophrenia Society helps individuals and families find their way in the mental health system. They also provide regional programs and services to help people with serious mental illnesses and their families. For more, visit or call 1-888-888-0029.


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