Prolonged Cannabis Use Associated With Psychosis

Young adults who are long-time users of cannabis appear more likely to develop psychosis.

The Study

3,801 young adults, born between 1981 and 1984, were assessed on cannabis use and psychotic outcomes when they were on average 20.1 years old. Analysis of the data showed that the longer participants had used cannabis, the more likely they were to have psychosis-related outcomes. Use of cannabis for 6 or more years, beginning around age 15, doubled a participant's risk of developing a non-affective psychosis and quadrupled the likelihood of scoring high on the Peters et al Delusions Inventory (a measurement of psychotic outcomes).

What Does This Mean

This is not the first study to find a link between cannabis use and psychosis, but prior studies haven't adequately controlled for other variables that might be responsible for the results. This new study reinforces the findings or previous studies, but shows that the link between cannabis use and psychosis is complex and does not prove a causal relationship. However, the researchers did find a few interesting new results:

• A look at sibling pairs among the participants showed that the association was unlikely to be due to genetic or environmental influences.
• Participants who had previously experienced hallucinations were more likely to begin using cannabis.

While the precise relationship between long-term cannabis use and psychosis remains unclear, it is apparent that one does exist.