Cannabis’s effects on memory can last up to two days, says U of A study

The study compared the cognitive skills of 120 adults who abstained from cannabis use for different amounts of time

A study conducted by a University of Alberta professor has finished collecting data on how long it takes to recover cognitive skills after using cannabis.

From October 2017 to October 2018, professor Scot Purdon from the faculty of medicine and dentistry tested 120 healthy adults who used one gram of marijuana a week to see if there were differences in their cognitive abilities after a period of abstinence. The study has yet to be submitted to a peer-reviewed journal.

Purdon wanted to understand what the effects of cannabis could have on his young adult patients to provide more accurate information.

“We know when you’re intoxicated on cannabis that it has quite significant changes on how you think, feel, and to some extent how you behave,” Purdon said. “What we don’t know is how long these effects will last. It’s a very, very important question when it comes to impaired driving or workplace health and safety.”

In the study, groups were created based on whether the participants abstained from cannabis use for one, two, or between three and seven days. The participants were then tested for several hours on their attention, memory, and planning skills. When the three groups were compared, Purdon found that those who abstained from cannabis use longer retained information better, and some could recover to normal levels in two days.

Purdon said he was also surprised by the difference between a person’s subjective description of their impairment compared to the measured results, as they did not perform as well as they thought they did.

“I think one important consequence of this work, potentially, is that you can recover from the effects of cannabis use and that the effects may not be permanent,” Purdon said. “The other is there’s a very real cognitive limitation associated with cannabis use, and we really don’t know for sure how long it lasts.”

Since the study is an observational study and not an experiment, Purdon said there may be other ways to interpret the data. Additionally, the results could be affected by untested variables like the quality and quantity of the cannabis used, as well as the different tolerance levels between individuals.

It’s a very preliminary study, to be completely frank about it. It’s a first step to understanding the duration of abstinence as it relates to cognitive limitations,” he said.

Although Purdon thinks that cannabis is under-studied at the moment, especially due to the lack of a test that could correlate lingering cannabis in the body to impairment, he is optimistic that legalization will lead to more research in the coming years.

“Ideally, we’d want to randomly assign people to short-term and long-term abstinence and then examine them through time prospectively or longitudinally,” said Purdon. “That’s quite an expensive study as you can imagine,  but that would be a very important next step.”

While data analysis is still ongoing, Purdon hopes to submit it to a peer-reviewed journal by Christmas, and to continue investigating the effects of cannabis in the future.

“There are so many questions that need to be answered when it comes to the psychological effects of cannabis not just cognitively, but in terms of mood and the effects of depression and anxiety,” Purdon said. “I think those are also very important questions that I would love to pursue.”

Jonathan Hocnalon

Jonathan Hocnalon is a fourth-year immunology student. He believes everyone's got a story to share: it's just a matter of finding the right questions, knowing when to ask them, and listening respectfully.

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