Cannabis Use Connected to Worsening Memory, Slower Reaction Time: Study

July 23, 2019 Updated: July 23, 2019

Regular use of cannabis can cause decreased performance in both memory and reaction speed compared to people who don’t partake of the drug, a recent study from McMaster University has found.

McMaster researchers took data collected from the participants of the Human Connectome Project, a U.S.-based study focused on the biology of the human brain, and used the people who had tested positive in a urine drug screening for tetrahydrocannabinol (THC), a psychoactive chemical found in cannabis. They then examined these people’s performance results on a series of cognitive tests in comparison to the results of people who hadn’t tested positive in the screening.

The results showed a significant relationship between cognitive performance and the use of cannabis—namely, that those who used cannabis performed worse on tests related to episodic memory and reaction time.

Although the research suggests that these effects don’t persist once THC has left the body, psychiatry professor James Mackillop, who led the study, says the drug can “stay in your system for a month if you’re a heavy user.” Cannabis is different to alcohol in that it is digested slowly, meaning that it has the capability to remain in a user’s bloodstream for long periods of time after ingestion.

“There are clear lingering effects,” MacKillop told The Toronto Star. “Not huge and not everywhere, but lingering effects nonetheless. If the stakes are very high and split-second performance really matters, these small effects could be meaningful.”

The introduction to the study says cannabis  is  one  of  the  most  commonly  used  psychoactive  drugs in the world, noting that use is increasing among young people  and  “may  escalate  further  with  legalization  of  recreational  use  in  several  states  in  the  United  States  and  nationwide  in  Canada.”

“Frequent cannabis  use  has  been  associated  with a number of adverse health consequences, such as  motor vehicle  injuries,  cannabis  use  disorder,  increased  risk  of psychotic disorders and chronic bronchitis,” the authors wrote. “There  is  also  considerable  concern  about  the  adverse  effects  of  cannabis  use  on  cognitive  abilities,  such  as  memory,  attention,  and  learning.”

Spike in Alcohol-Linked ER Visits in Ontario

Another drug-related study shows that emergency room visits due to alcohol-related health issues have been rising sharply in Ontario, particularly among women and young adults.

The Canadian Medical Association Journal (CMAJ) study, published July 22, analyzed data from 2003 to 2016 and included more than 15 million individuals living in Ontario between the ages of 10 and 105. In that 14-year period, researchers found there were a total of 765,346 emergency room visits attributable to alcohol use. The increase in these alcohol-related visits was about 4.4 times greater than the increase in the overall number of ER visits.

Additionally, there were some worrying statistics in two specific groups: visits by women increased by 86 percent during the study period, and visits by individuals aged 25 to 29—which the researchers categorized as young adults— increased by 175 percent, the largest overall change observed in the study.

A comprehensive infographic provided by CMAJ sums up the statistics involved in their Ontario study on alcohol-linked ER visits. (Canadian Medical Association Journal)

In the 25-to-29 group, the rate of ER visits attributable to alcohol use jumped by 240 percent in women and 145 percent in men.

The study tracked the ER visits by looking at the system created by the Canadian Institute for Health Information. Hospitals in Ontario use diagnostic codes to classify and categorize their data, and the numbers in the study came from emergency room visits that were indicated as “hospitalizations entirely caused by alcohol.”

Among these hospitalizations, 44.6 percent were for intoxication, 21.4 percent for harmful use, 11.4 percent for withdrawal, and 10.9 percent for alcohol dependence. The most common medical harms associated with these causes included alcoholic liver disease and alcohol poisoning.

Dr. Daniel Myran, the lead author of the CMAJ study and a family physician, said he had expected to see increases, but not to such a “surprising” extent.

“I find these increases alarming, and I think that policy-makers should find these increases alarming,” he told CTV News.

Myran is a resident with the University of Ottawa’s School of Epidemiology and Public Health and has a history of focusing his research on alcohol-related issues in Canada.

In an April op-ed in The Globe and Mail, he criticized the previous Ontario Liberal government’s loose policies on alcohol distribution, and referred to another recent study he led that was published in the research journal Addiction in March.

“When we compared the two years before and two years after the policy took effect, we found a 17.8 percent increase in the number of emergency-room visits due to alcohol, compared to the 6.2 percent growth of all types of ER visits,” Myran wrote. “Areas of the province that had grocery stores selling alcohol had a 6 percent greater increase in the rate of ER visits due to alcohol than areas that did not.”

While the newer study’s interpretations maintain that government policies continue to play a major role in these statistics, it also mentions the possibility of marketing being a factor, saying that a contributor may be “increasing alcohol marketing and promotion,” which is “less tightly regulated in both Ontario and Canada.”

The CMAJ report says future work on the topic may explore the potential contribution of Ontario’s alcohol marketing to the rising numbers observed in the study.

Shery Spithoff, an addiction medicine physician at Women’s College Hospital, and a University of Toronto lecturer, proposes possible solutions to the spike in ER visits in a July 22 CMAJ commentary. She wrote that federal and provincial governments should “employ a public health approach to maximize benefits and minimize harms,” including but not limited to strictly controlling the sale and distribution of alcohol, implementing taxes and price minimums, and putting regulations on the marketing and branding of alcohol use.

“At minimum, governments should consider applying the rules it uses for tobacco promotion to alcohol,” Spithoff wrote. “There is no reason to treat alcohol—a substance at least as harmful—differently.”

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