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Cannabis Use Before Bedtime Does Not Cause Next-Day Impairment Of Cognitive Ability Or Driving Performance, Study Shows



A new study suggests that using marijuana before sleep has minimal if any effect on a range of performance measures the next day, including simulated driving, cognitive and psychomotor function tasks, subjective effects and mood.

The report, which drew data from a larger study investigating the effects of THC and CBD on insomnia, looked at outcomes from 20 adults with physician-diagnosed insomnia who infrequently used marijuana.

“The results of this study indicate that a single oral dose of 10 mg THC (in combination with 200 mg CBD) does not notably impair ‘next day’ cognitive function or driving performance relative to placebo in adults with insomnia who infrequently use marijuana,” says the paper, from researchers at Macquarie University in Sydney, the University of Sydney, Royal Prince Alfred Hospital in Sydney, Gold Coast-based Griffith University and Johns Hopkins University.

“The use of cannabis by night as a sleep aid is highly prevalent and there are legitimate concerns that this may lead to impaired daytime (‘next day’) function, particularly on safety sensitive tasks such as driving,” the 11-author team wrote in the report published last week in the journal Psychopharmacology.

Results, however, showed “no differences in ‘next day’ performance in 27 out of 28 tests of cognitive and psychomotor function and simulated driving tests relative to placebo.”

“We found a lack of notable ‘next day’ impairment to cognitive and psychomotor function and simulated driving performance.”

Participants were randomly given either a placebo or 2 milliliters of cannabis oil containing 10 milligrams of THC and 200 mg CBD. Researchers said the THC amount was selected “based on prior studies showing that 10 mg oral THC produced discriminable subjective drug effects (e.g., increased ‘drowsiness’) without altering cognitive and psychomotor performance among infrequent cannabis users”—in other words, the amount someone might take if their goal was to use cannabis as a sleep aid.

In a second lab visit, participants who received the placebo were given the THC–CBD mixture, while those who had the cannabis oil were given the placebo.

Cognitive tests were administered within two hours of participants waking, while driving performance, which was measured through a fixed-base driving simulator, was tested 10 hours after administration. Subjects were also asked how about experienced effects—for example how “stoned,” “sedated,” “alert,” “anxious” or “sleepy” they felt—at baseline and then after 30 minutes, 10 hours, 12 hours, 14 hours, 16 hours and 18 hours.

“Almost all of the cognitive tests conducted, involving attention, working memory, speed of information processing, and other domains, showed no ‘next day’ effects of THC/CBD,” the report says.

No significant differences were seen between the THC–CBD and placebo results in 27 of the 28 cognitive performance tasks. There was what researchers described as “a small reduction in percentage accuracy”—about 1.4 percent—in the so-called Stoop color and word test, a measure of cognitive interference, however, but researchers said that finding was “not clinically meaningful” because both groups demonstrated “a very high percentage of accuracy (i.e., >97%)” on the test.

“Importantly, no significant difference in accuracy was observed on the more difficult ‘hard/incongruent condition’ of the Stroop-Word Test, which requires participants to match the meaning of the word presented, not the printed colour of the word,” authors added. “For comparison, the morning after alcohol consumption (i.e., the hangover state) produced significantly greater interference on the Stroop-Word Test, but not the Stroop-Colour Test, relative to the alcohol-free control group (i.e., no hangover state).”

No differences were observed in terms of driving performance, meanwhile.

“None of the simulated driving outcome measures were significantly different between THC/CBD and placebo,” the study says, adding: “This is consistent with our recent meta-regression analysis, which concluded that driving-related skills in occasional cannabis users recover within ~8 h after ingesting 20 mg oral THC.”

“There were no impairing effects of THC/CBD given by night on simulated driving performance assessed the following morning at ~10 h post-treatment; coinciding with a time that many people might commute on roads (e.g., driving to work in ‘rush-hour’),” the authors wrote.

By contrast, they noted that”commonly prescribed sedative-hypnotics are known to impair next-day function,” pointing as examples to benzodiazepine and zopiclone.

The researchers acknowledged the relatively small sample size of the study and that the findings were based on only a single dose of cannabis oil.

“This precludes any conclusions regarding the effects of repeated dosing with THC, with or without CBD, on daytime function in insomnia disorder, which is more representative of how some people use medical cannabis for sleep in the community,” they wrote. “However, it is hypothesized that the chances of detecting ‘next day’ impairment are less likely with repeated dosing due to the development of at least partial tolerance to the impairing effects of THC.”

Though some cannabis users anecdotally report feeling residual effects of cannabis use the day afterward, another recent study found no evidence that marijuana consumption causes a hangover the next day.

A report published last December, meanwhile, examined neurocognitive effects in medical marijuana patients, finding that “prescribed medical cannabis may have minimal acute impact on cognitive function among patients with chronic health conditions.”

Another report, published March in the journal Current Alzheimer Research, linked marijuana use to lower odds of subjective cognitive decline (SCD), with consumers and patients reporting less confusion and memory loss compared to non-users.

A separate 2022 study on marijuana and laziness found no difference in apathy or reward-based behavior between people who used cannabis on at least a weekly basis and non-users.

A Washington State University study published late last year found that most cannabis consumers with sleep issues preferred to use marijuana instead of other sleep aids to help get to bed, reporting better outcomes the next morning and fewer side effects. Smoking joints or vaping products that contained THC, CBD and the terpene myrcene were especially popular.

“Unlike long-acting sedatives and alcohol, cannabis was not associated with a ‘hangover’ effect,” an author of that study said, “although individuals reported some lingering effects such as sleepiness and changes in mood.”

Quality of sleep often arises in other studies into the potential benefits of marijuana, and generally, consumers say it enhances their rest. Two other 2023 recent studies, for example—one involving people with chronic health conditions and another looking at people diagnosed with neurological disorders—found that sleep quality improved with cannabis use.

Marijuana Use Linked To Increase In Light Physical Activity, Study Challenging ‘Lazy Stoner’ Stereotype Finds

Photo courtesy of Carlos Gracia.

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Ben Adlin, a senior editor at Marijuana Moment, has been covering cannabis and other drug policy issues professionally since 2011. He was previously a senior news editor at Leafly, an associate editor at the Los Angeles Daily Journal and a Coro Fellow in Public Affairs. He lives in Washington State.


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