By DB Recovery Resources, Published: February 16, 2015

King’s College London research by 23 scientists also blames ‘skunk’ for 1 in 4 of all new serious mental disorders. Read the report.


High potency marijuana use alone was also responsible for 24% of psychosis cases in the south London study group.

LONDON, ENGLAND – Today, in one of the most prominent medical journals in the world, Lancet Psychiatry, a team of 23 scientists published a large study showing that people who smoked high-grade marijuana – about 16% THC with no CBD, similar to average US varieties of marijuana – were five times as likely than non-users to have a psychotic disorder. Weekend users were three times as likely than non-users to have a psychotic disorder, and high potent marijuana use alone was responsible for 24% of those adults presenting with first-episode psychosis to the psychiatric services in south London.

Sir Robin Murray, Professor of Psychiatric Research at the IoPPN at King’s and senior researcher on the study stated, “It is now well known that use of cannabis increases the risk of psychosis. However, skeptics still claim that this is not an important cause of schizophrenia-like psychosis.

“This paper suggests that we could prevent almost one quarter of cases of psychosis if no-one smoked high potency cannabis. This could save young patients a lot of suffering and the Health Services a lot of money.”

Between 2005 and 2011, researchers worked with 410 patients aged 18-65 who reported a first episode of psychosis at the South London and Maudsley NHS Foundation Trust. A further 370 healthy participants from the same area of South London were included as controls.

A main finding was that the frequency of use and cannabis potency, which are often overlooked when determining how harmful the drug can be, are essential factors in the mental health effects on users. These factors are not sufficiently considered by doctors.

“As with smoking tobacco and drinking alcohol you need a clear public message,” said Dr. Di Forti, the lead author of the study.

The findings have been noted across the Atlantic. “For years, the marijuana industry has discounted the link between the highly potent strains of marijuana they produce and mental health problems,” commented Dr. Kevin A. Sabet, President of SAM and the Director of the Drug Policy Institute at the University of Florida. “Big Marijuana – who relies on addiction for profit – will of course discount this study too, but the public and lawmakers should not be deceived. More marijuana use equals more mental health problems, no matter what special interest lobbyists want us to think. We must urgently get this information out now to every lawmaker in the country.”