A new study published in the British Medical Journal, surveying health records for more than 30,000 people over the course of six years, has found that cannabis users were 22 percent more likely than nonusers to visit an emergency department or be hospitalized.
From the study’s conclusion:
Although no significant association was observed between cannabis use and respiratory-related ER visits or hospitalisations, the risk of an equally important morbidity outcome, all-cause ER visit or hospitalisation, was significantly greater among cannabis users than among control individuals. Therefore, cannabis use is associated with increased risk for serious adverse health events and its recreational consumption is not benign.
Though studies like these are worth reading, it’s important to keep in mind that quantity (in sample size) can’t compensate for quality. A well-designed random sample of individuals followed prospectively, with thought and care going into how to design the study to minimize biases, is preferable to a large retrospective data set.
Of course, the two ought not to be mutually exclusive. For instance, the two studies I summarized in my “Big Dope” cover story for the U.S. edition of the Spectator are very robust:
A 2008 article in World Psychiatry, the top journal in the field, outlines the results of a 15-year prospective study in Sweden examining schizophrenia in over 50,000 Swedish conscripts. It found during its 27-year followup that, if the association they identify was indeed causal, ‘13 percent of cases of schizophrenia could be averted if all cannabis use were prevented’. A more recent 2019 study in the Lancet Psychiatry examined patterns of psychotic incidence across Europe in connection to cannabis use, and found that ‘daily cannabis use was associated with increased odds of psychotic disorder compared with never users, increasing to nearly five-times increased odds for daily use of high-potency types of cannabis’. Moreover, they concluded that, assuming this association was causal (which the authors consider highly credible), as much as ‘20 percent of the new cases of psychotic disorder across all our sites could have been prevented if daily use of cannabis had been abolished’.