High potency cannabis use linked to psychosis finds study

By Dr. Ananya Mandal, MDMar 20 2019

With more and more states and regions legalizing the use of medical marijuana or cannabis, experts are also looking at the long term effects of marijuana use and its safety. According to a new study published this week in the journal The Lancet Psychiatry, frequent use of marijuana can lead to psychotic episodes.

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According to the researchers “high potency cannabis” especially contain over 10 percent tetrahydrocannabinol or THC. THC is the main compound in cannabis that is responsible for the psychoactive effects of the drug. High levels of THC exposure is associated with long term effects on the psyche say experts. The high potency cannabis is called skunk in the UK. The European Monitoring Center for Drugs and Drug Addiction and national data from the different countries created a database on the THC content of each of the products. Locally produced Dutch resin Nederhasj for example contains as high as 67 percent of THC.

The authors noted that certain regions in London, Paris and Amsterdam have a higher incidence of new cases of psychosis. These are also regions where the high potency cannabis is available. They looked at 901 people aged between 18 and 64 years. These participants were diagnosed with their first episode of psychosis between May 2010 and April 2015. They were all residents of one of the 11 cities where the study took place. These cities were Amsterdam, Barcelona, London, Paris, other European cities and one city in Brazil. Apart from these participants, over 1200 healthy controls were also included in the study. Both groups were compared in terms of their cannabis use. Study author Marta Di Forti, psychiatrist and clinician scientist at King's College London, said, “We asked people if they used cannabis, when did they start using it and what kind of cannabis.”

Results revealed that those who regularly used cannabis were three times more likely to have psychotic episode compared to those who did not use the drug. The risk was raised in individuals who started smoking cannabis from the age of 15 or less. Di Forti said that high potency cannabis doubled the risks of getting psychosis. Daily users of high potency cannabis had a four times elevated risk of psychosis, the researchers said. Di Forti said, “…twenty years ago, there wasn't much high potency cannabis available [in the market].”

Suzanne Gage, a psychologist and epidemiologist at the University of Liverpool, in an accompanying commentary with the study said, “What this paper has done that's really nice is they look at rates of psychosis and cannabis use in lots of different places where underlying rates of psychosis are different.” She added that the connection between the cities where high potency cannabis is available and incidence of psychosis has not been studied before. She said, “That's a really interesting finding and that's not something anyone has done before.”