UK Study – Marijuana use linked to serious mental illness

A new study finds “highly significant associations between cannabis use and increased risks of developing common and severe mental illnesses.” In fact the results were alarming. Despite there being a “gross under-recording of cannabis use in GP records”  this extensive study found that marijuana use was associated with almost seven-fold risk of developing a serious mental illness such as schizophrenia, bipolar disorder, or other psychoses.

Researchers in the UK analysed a database compiled by clinicians containing 10,489,571 records of patients from 787 general practices. All were eligible to participate in their study. Of those, 28,218 had a recorded exposure to marijuana use. These patients were matched to 56,208 patients who had no recorded exposure to the drug. The database provides data not only about marijuana use and diagnosed mental disorders, but also information about prescription medications used to treat such disorders.

The researchers say to their knowledge their study is the first attempt to examine the relationship between marijuana use and the development of mental illnesses or future use of medication to treat such illnesses. During a three-year follow-up period, they found that marijuana use was associated with:

  • a four-fold risk of developing any mental disorder,
  • a two-to-three-fold risk of developing anxiety or depression, and
  • an almost seven-fold risk of developing a serious mental illness such as schizophrenia, bipolar disorder, or other psychoses.

This is deeply troubling and points to serious mental health illness later in life.

“In order to prevent mental ill health in later life and decelerate the increasing trend in disease burden, primary care clinicians need to actively enquire about, monitor, and discourage the use of cannabis in young people who may be particularly vulnerable,” they conclude.

Read full text of this Psychological Medicine study here.

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