The Next-Day Effects of Cannabis Use

Every year, about 200 million people use cannabis for its euphorigenic effects, or more recently, to reduce the symptoms of chronic pain, insomnia, or anxiety. I have written extensively about the dose- and age-dependent benefits and risks of cannabis use. Without a doubt, THC can acutely, dose-dependently impair cognitive function and psychomotor performance. These impairments include slowed reaction time, impaired working memory, and an inability to divide one’s attention between tasks. The presence of THC in the brain can also increase the risk of judgment errors, accidents, and injury when operating a motor vehicle.

One very important factor that has not been fully explored is the duration of THC-induced impairments. For example, how long should someone wait after using cannabis before performing safety-sensitive or complex tasks?

Regular Cannabis Users Have a Shorter Window of Impairment

One analysis outlined a period of impairment that ranged from three to 10 hours after THC exposure. The precise duration depended on the dose, route of administration, and the regularity of THC use. High doses lasted longer; oral administration lasted longer since gastrointestinal absorption is slower than pulmonary absorption; however, inhalation produces a faster intoxication with higher overall blood levels.

Regular cannabis users will have a shorter window of impairment than occasional users because of their more efficient metabolism of THC by the liver and other tissues. Regular users thus appear to be more tolerant to the cognitive impairing effects of THC. These factors must be considered when examining the “next day” effects of any psychoactive drug.

Multiple Studies Show No ‘‘Next Day’’ Effects of THC

Some government agencies warn that THC-induced impairments may persist for more than 24 hours. This concern by employers can impact workers who use medicinal cannabis during the evening or weekend to treat their insomnia and chronic pain (the two most common medical uses of cannabis products). However, such advice was not derived from the current scientific evidence. A recent study conducted a systematic review of the ‘‘next day’’ (longer than 8 hours after administration) effects of THC use on cognitive function and the performance of complex tasks, such as performance in a flight simulator.

Twenty published studies that utilized 345 performance tests were reviewed. The studies varied in design, dose, and duration of the delay in performance testing. Most studies administered a single dose of THC (about 11 to 26 mg) and examined performance in regular cannabis users between 12 and 24 hours after administration.

The majority (209 out of the 345 total) performance tests conducted showed no ‘‘next day’’ effects of THC. Most of these studies used randomized, double-blind, placebo-controlled designs. Interestingly, 88 out of 209 tests failed to demonstrate ‘‘acute’’ (occurring less than 8 h after drug treatment) impairments due to THC.

Five studies did report impairing “next day” effects of TH, however, these five studies failed to use randomized, double-blind, placebo-controlled designs. In contrast, three studies reported significant “next day” effects of THC, however, two of these studies had a ‘‘high risk’’ of experimenter bias and were conducted over thirty years ago during a time of considerable bias.

Two recent studies that were considered the best designed and conducted, that also employed good-quality research methods using randomized double-blind, placebo-controlled trials, confirmed that high doses of inhaled THC (up to 100 mg) did not impair ‘‘next day’’ performance in regular cannabis users.

In summary, although a few lower-quality studies reported the ‘‘next day’’ effects of THC on cognitive function, most higher-quality studies reported no such effects. Overall, this systematic review of published studies found little high-quality scientific evidence to support the assertion that cannabis use impairs ‘‘next day’’ performance.

Placebo Essential Reads

Placebo Effects and Direct-to-Consumer Advertising

Is Optimism the World's Most Powerful Placebo Effect?

In contrast, similar studies of the ‘‘next day’’ effects of alcohol use have shown that an ‘‘alcohol hangover’’ has a small to moderate detrimental effect on cognitive performance. These conclusions will need to be replicated in future studies using a greater number of regular cannabis users as well as those with no drug experience.

Facebook/LinkedIn image: BAZA Production/Shutterstock