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Those with positive THC tests had inferior scores in the areas of mental processing speed and episodic memory compared to those whose screenings showed no evidence of having recently consumed the drug.

Approximately 43 per cent of participants had never used cannabis, with another 28 per cent having only consumed it 10 times or less. Nearly 10 per cent of those interviewed currently or previously suffered from cannabis use disorder. “Positive urinary THC status was associated with worse performance in episodic memory and processing speed, and positive cannabis use disorder status was associated with lower fluid intelligence,” the study concludes.

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Researchers say that although further studies are needed, “this has implications for all cannabis users, especially medical cannabis users who may be consuming daily or multiple times daily for symptom management,” James MacKillop, one of the study’s authors and a researcher at McMaster, told Reuters.

“These individuals would likely have THC chronically circulating in their system and, in turn, cognitive consequences. This applies to heavy recreational users who are consuming daily too of course.”

The potential occupational hazards of cannabis consumption have been a point of contention in Canada of late, with some agencies and employers demanding 28 days of abstention from the drug before reporting to work.

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