The University of Sydney (UoS) announced its findings on Feb. 6, sharing that there isn’t any evidence of cannabis “hangovers,” or effects of cannabis that continues hours or days after consumption. The study is slated to appear in the print version of the journal Cannabis and Cannabinoid Research soon but is currently available for viewing online. The authors analyzed 20 different research studies that examined THC and its lingering effects, or lack thereof, at least eight hours after consumption occurred.
According to Dr. Danielle McCartney, UoS research fellow at the Lambert Initiative for Cannabinoid Therapeutics, there wasn’t much evidence of cannabis affecting individuals long term. “Most studies didn’t detect ‘next day’ effects of cannabis use, and the few that did had significant limitations,” McCartney said in a press release. “Overall, it appears that there is limited scientific evidence to support the assertion that cannabis use impairs ‘next day’ performance. Though, further research is still required to fully address this issue.”
Of the 20 studies reviewed, 61% reported no “next day” effects, 35% reported “unclear or unambiguous ‘next day’ effects,” and only 4% reported negative “next day” effects (which were noted as low-quality studies, or studies that were published over 18 years ago).
“We can’t really comment on the magnitude of these effects because they weren’t all that well reported,” McCartney said. “They didn’t appear to be associated with a specific dose of THC, route of THC administration or type of assessment.”
Pinpointing impairment in individuals continues to be a challenge for cannabis consumers, especially when it comes to detecting such effects on drivers or those who work in specific types of workplaces. “THC can persist in blood and oral fluid for an extended period of time,” McCartney explained. “So it is important to find out whether impairment can persist, too. People are being advised not to drive or perform other safety-sensitive tasks for 24 hours after cannabis use. However, we found little evidence to support this recommendation.”
The research authors cautioned legislators to consider how individuals who use medical cannabis, and are not impaired, still suffer from lack of accurate testing methods. “However, policy makers should bear in mind that the implementation of very conservative workplace regulations can have serious consequences (e.g., termination of employment with a positive drug test) and impact the quality of life of individuals who are required to abstain from medicinal cannabis use to treat conditions such as insomnia or chronic pain for fear of a positive workplace or roadside drug test,” the authors wrote.
Such evidence of this is seen in a study that appeared in Natural Scientific Reports in March 2022, which also found that THC levels in blood or breath tests do not correlate to impairment. The study was also led by McCartney, and also came to a similar conclusion. “Higher blood THC concentrations were only weakly associated with increased impairment in occasional cannabis users while no significant relationship was detected in regular cannabis users,” McCartney said. “This suggests that blood and oral fluid THC concentrations are relatively poor indicators of cannabis-THC-induced impairment.”
Many patients continue to be negatively affected by the lack of accurate testing, potentially preventing them from using cannabis as a medicine. A recent study from the University of Michigan found that 31% of adults use cannabis to treat chronic pain. Another study from December 2022 found positive effects of cannabis for those who suffer from bipolar disorder. The same goes for other psychedelics such as psilocybin, which was recently found to be beneficial to calm patients and help them when undergoing an MRI.