Cannabis and Psychosis

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Author: BC Schizophrenia Society


Marijuana use has been shown to trigger and worsen psychosis in young people who are vulnerable to psychosis and may even cause psychotic illnesses in people who would not otherwise suffer from them.

Can marijuana use trigger psychotic illnesses like schizophrenia?

Yes. There is increasing research evidence to show that, particularly when someone starts using marijuana in their teens and uses heavily, that marijuana can trigger early onset of psychotic illnesses. For those do become ill, approximately 15% will continue to have psychotic symptoms even after they stop using.

For people who are already vulnerable to psychosis, cannabis use has been shown to make people four times more likely to become ill with psychosis. They are also likely to experience their first symptoms at a younger age.

The younger a person is when they experience psychosis, the more severe damage will be, and the more difficult recovery is. The brain is still developing, and therefore much more vulnerable, until a person's mid-twenties.

According to experts on psychosis, heavy cannabis use past or present is involved in 70% of those cases of psychosis that are very severe or do not respond well to treatment.


What does marijuana do to the brain of someone vulnerable to psychosis?

Marijuana stimulates the release of dopamine, a neurotransmitter (chemical that moves information in the brain and body). Increased dopamine is thought to be part of the problem in brains affected by schizophrenia.

Brain scans comparing a person whose brain has been damaged by marijuana with one whose brain has been damaged by schizophrenia show that marijuana and schizophrenia both restrict blood flow in the brain.


Does using marijuana prevent me from recovering from psychosis?

Yes. if you want to recover, you will need to stop. For someone with a psychotic illness, using marijuana:

  • Makes symptoms worse

  • Blocks the effects of medications, making it necessary to take higher doses, which leads to more side effects.

  • Causes more 'secondary symptoms' like anxiety, depression and memory problems

  • Is likely to trigger a relapse and prevent recovery.

We know that most people with schizophrenia who use marijuana have worse symptoms, a more difficult recovery and more hospitalizations than people who don't use at all. Of persons with psychotic illness which don't respond to treatment, 70% or more are using cannabis or other street drugs.


Ways others have found useful to help them quit

Find substitutes for things the drug used to provide. For example plan other activities to deal with boredom or loneliness.

  • Come up with a script to use to turn down drugs if offered.

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

  • Spend time with friends who don't use.

  • See friends who do use in places where using will be unlikely.


How to Get Help

Ask your doctor or mental health service provider about 'dual diagnosis' programs in your area.

  • Ask specifically for services that are equipped to help people with mental illness. Not all alcohol and drug treatment services are knowledgeable about the needs of people with mental illness.

  • Keep your doctor informed about your drug and alcohol use. As you reduce or eliminate your street drug or alcohol use, your medication dosage may need to be reduced or changed.

  • As someone with a mental illness, it is important to be wary of drug and alcohol services or support groups that suggest or require going off your prescribed medication.

Always consult with your doctor before changing medication dosage or going off medication.

You don't have to deal with this alone. Help is available.


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.