Skip to content

    Health & Balance

    Font Size

    Pot May Cause Depression, Schizophrenia

    Strongest Evidence Yet that Marijuana May Lead to Mental Illness
    WebMD Health News

    Nov. 21, 2002 -- Three newly published studies link frequent marijuana use at a young age to an increased risk of depression and schizophrenia later in life. The studies offer some of the best evidence yet that smoking marijuana can influence the progression of mental illness.

    Past research has linked pot smoking with depression and schizophrenia. But it has been unclear whether marijuana use causes psychosis or whether those prone to psychosis self-medicate with the drug. The new studies, published in the Nov. 23 British Medical Journal, suggest a direct link between frequent marijuana use and psychiatric illness that is not explained by self-medication.

    "Most [earlier] studies suggested that mental illness in not a result of using marijuana, but the other way around," child and adolescent psychiatrist Joseph M. Rey, MD, PhD, tells WebMD. "These [new] studies do not disprove the self-medication theory completely. But they offer strong support for the explanation that cannabis use causes both schizophrenia and depression."

    In an editorial accompanying the studies, Rey notes that it is not yet clear whether marijuana use triggers mental illness in otherwise vulnerable people or if it causes these conditions in people who are not predisposed to them.

    In the largest of the newly reported studies, researchers followed about 50,000 Swedish men for 27 years after being drafted for military service. All of the recruits underwent a psychological evaluation, which included questions about drug use, upon entering the service at age 18.

    Those who reported smoking marijuana more than 50 times were three times more likely to develop schizophrenia over the next three decades as those who did not use the drug. The association was dose-dependent, with those who smoked pot five to 10 times having only a slightly increased risk. No association was seen between alcohol use and later schizophrenia.

    "We cannot be certain that the increased risk we saw is due to cannabis use, but it is the most likely explanation," psychiatrist and lead researcher Stanley Zammit tells WebMD. "It is important to point out that the risk is still quite small. If your lifetime risk of developing schizophrenia is 1% then frequent use of cannabis would increase that risk to 3%."

    Today on WebMD

    woman in yoga class
    6 health benefits of yoga.
    beautiful girl lying down of grass
    10 relaxation techniques to try.
    mature woman with glass of water
    Do you really need to drink 8 glasses of water a day?
    coffee beans in shape of mug
    Get the facts.
    Take your medication
    Hand appearing to hold the sun
    Hungover man
    Welcome mat and wellington boots
    Woman worn out on couch
    Happy and sad faces
    Fingertip with string tied in a bow
    laughing family