Image credit: Chmee2

Think. Discuss. Act. Marijuana

Print Friendly and PDF

Review: Cannabis Risk Boosts Pyschosis

Hopkin, Michael, “Cannabis boosts risk psychosis: Teens vulnerable to mental problems should abstain, experts warn,”  [email protected], 1 Dec 04.  seen 1 Feb 05
“Marijuana may increase risk of psychosis: Drug makes some users more vulnerable to mental problems.”   Reuters through MSNBC posted 1 Dec 04; last seen 1 Feb 05.


These articles highlight the findings of Dutch Professor Jim van Os of Maastricht University in the Netherlands. He and his colleagues studied 2,437 youth (age 14-24.) The study can be found online in the British Medical Journal.

Prof. van Os and his colleagues determined whether or not 2,437 young people had a disposition for psychosis, and their use of cannabis. Respondents were followed up after four years.

The findings of this study:

1. “Cannabis does not act in the same fashion on psychosis risk for everybody. There is a group that is particularly susceptible,” Professor Van Os told a news conference.
2. Young smokers with a family history, or pre-existing susceptibility to mental instability, are particularly vulnerable to negative effects of marijuana.
3. “The results show that in the group without vulnerability to psychosis, there was a small effect of cannabis on the onset of psychotic symptoms four years later. But the risk was four times bigger in individuals who had a personal vulnerability to psychosis,” the Professor said.
4. “If you are vulnerable, then the more cannabis you use, the greater your risk of psychosis,” van Os said.

These scientists concluded that frequent youthful users of marijuana or cannabis increase the risk of delusions or bizarre behavior later in life. “Cannabis use moderately increases the risk of psychotic symptoms in young people but has a much stronger effect in those with evidence of predisposition for psychosis.”

These finding are consistent with all other studies on this particular aspect of marijuana smoking.

“We’re not saying that cannabis is the major cause of psychosis,”  one of the experts, Robin Murray of the Institute of Psychiatry in London said. Other factors of stress such as emigrating may have greater effect.

How cannabis increases the risk of mental illness is not clearly understood by the medical profession, but doctors suspect it negatively affects the brain’s dopamine system which is associated with pleasure. More technically, the neuroscientists sense that the main psychoactive ingredient, delta-9-tetrahydrocannabinol (THC) stimulates the brain to release more of the neurotransmitter dopamine which initially stimulates pleasure but can lead to later paranoia or hallucinations.

“There’s a shortage of knowledge and training” (among psychiatric care-givers) says Zerrin Atakan (also of the Institute of Psychiatry). “What I see as a clinician is that patients see the connection at first (between abuse of cannabis and mental problems), but when they start to get better they remember the pleasurable aspects of cannabis.”

Van Os points out a further problem that illegal drug peddlers sell cannabis containing widely differing levels of THC. “In the Netherlands concentrations are getting very high, up to 20% in some places. Youngsters think this is normal, but many of the old hippies in Amsterdam refuse to take it; they are used to 2 or 3%.”

These experts have different opinions as to whether or not cannabis should be made legal. Arguments on both sides of this debate are given elsewhere.

Questions for Reflection and Discussion

  1. Do you know anyone who has developed psychosis from using marijuana?
  2. How can the results from this study be used to inform your discussions with teens around using marijuana?
  3. Besides psychosis, what are the other negative effects of using marijuana?


  • Marijuana is a powerful substance which has various side affects. This one in particular gives greater evidence to abstaining from its use and kids, especially those predisposed to psychosis, should be informed.

© 2018 CYS

Write a Reply or Comment

Your email address will not be published. Required fields are marked *