Heavy Marijuana Use Associated With Three Times Higher Risk of Psychosis


People who smoke high-potency marijuana, especially if they do so daily, are at a three to five times greater risk of experiencing hospitalization for psychosis than people who smoke low-potency marijuana or no marijuana at all, according to research in The Lancet Psychiatry.

The team of Kings College London researchers studied 410 patients with first-episode psychosis and 370 population controls in an area of South London, England between May 1, 2005, and May 31, 2011.

Researcher Sir Robin Murray told The Guardian that the study provided “clear evidence” for a “causal link” between smoking strong cannabis and the risk of mental illness. “The argument initially was that the people who are going to smoke cannabis are a bit odd anyway,” said Murray. “In south London, two-thirds of people have used cannabis and it seems unlikely that two-thirds of people are abnormal.”

Smoking skunk cannabis triples risk of serious psychotic episode, says research (The Guardian, February 16, 2015)

Di Forti, Marta, Arianna Marconi, Elena Carra, Sara Fraietta, Antonella Trotta, Matteo Bonomo, Francesca Bianconi, et al. “Proportion of Patients in South London with First-Episode Psychosis Attributable to Use of High Potency Cannabis: A Case-Control Study.” The Lancet Psychiatry. Accessed February 17, 2015. doi:10.1016/S2215-0366(14)00117-5. (Abstract and full text)


  1. It is worrying but not as much as the fact that instead of getting a detox and being advised to stay away from marihuana in the future most of these people will most likely be put on even worse drugs and labelled as incurably ill.

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  2. Guess the results of this study from King’s College London which has been published in the very well-regarded Lancet journal doesn’t come as any surprise to this mom who desperately tried to convince the so-called MH “experts” to just read the plethora of scientific papers, globally, re:cannabis-psychosis link in Oct’09 & again in May ’11 when my first-born son suffered two episodes of psychosis. Both episodes came out of nowhere, literally overnight, but my than just turned 23 yr old son (2009) admitted to using cannabis ( apparently used more frequently after a serious boating accident/serious knee injury with surgery and extensive rehab) unbeknownst to his parents until his 1st episode psychosis. But instead of looking at the obvious- my son’s use of cannabis & his toxicology report was (+) for THC the p-docs boxed this beautiful young man with NO history of MI “bipolar for life, meds for life”…yet the research I found online suggested marijuana was the culprit. No-one believed the research ( just reinforces the arrogance of society!!!) and what I sadly learned too late- many pot users are dependent on today’s pot since ( according to the Netherland’s & Australian researchers pot strains with at least 15% THC create addictive qualities on par with heroin & cocaine). Sad I had to lose my extremely beloved, extroverted son who had many successes in life before using pot since it’s such a part of this youth culture. His many friends & family mourn his tragic death, by suicide, 37 months ago ( having been off all psychotropics & THC). http://www.telegraph.co.uk/news/health/news/11414605/Super-strong-cannabis-responsible-for-quarter-of-new-psychosis-cases.html

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    • I’m very sorry for your loss, larmac. And I agree, it is criminal that the psychiatric profession is misdiagnosing the adverse effects of drugs as “lifelong, incurable, genetic mental illnesses.” I, too, ran into sick and unethical doctors who misdiagnosed the adverse effects of drugs they gave me (Wellbutrin for smoking cessation, Voltaren for inflammation due to a “bad fix” on a broken bone by my PCP’s husband, and Ultram, which I rarely took) as “bipolar.”

      These unethical doctors then made me psychotic via neuroleptic induced “anticholinergic intoxication syndrome … Central symptoms may include memory loss, disorientation, incoherence, hallucinations, psychosis, delirium, hyperactivity, twitching or jerking movements, stereotypy, and seizures.”

      The doctors are killing too many people. And defaming, discrediting, and torturing too many for their own personal, greedy little reasons. Based upon my medical records, it does seem that the psychopaths have found their way into the psychiatric profession and mainstream medical community.

      Is it wise for societies to give unchecked power to psychopaths? I think not. But we have, from the psychopaths who have found their way into the “helping professions” to the corporate heads, who are legally required to behave in the best interest of the stockholders rather than those purchasing their products (like the pharmaceutical industry). We currently live in a world controlled by psychopaths.

      How do we get the psychopaths out of power? Break up the big businesses? Go back to a competitive market economy? Make it illegal for doctors to diagnose people with “mental illnesses” that have no scientific validity? Make it illegal for doctors to prescribe drugs that cause the symptoms of their fictitious “mental illnesses,” perhaps?

      My best to you, larmac, and I am truly sorry for your loss. It’s criminal, and your son’s doctors belong in jail.

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    • RE “according to the Netherland’s & Australian researchers pot strains with at least 15% THC create addictive qualities on par with heroin & cocaine”

      I have been around the addictions field for a long time and that is absurd, it’s drug war propaganda to boost funding.

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