With the decriminalization of cannabis comes a list of questions and concerns about the medical and recreational use of cannabis—including how long the drug’s effects actually last.
While society has had decades to question the link between alcohol consumption and poisoning, the duration of damage from inhaling or consuming weed is more anecdotal than scientific.
THE meta-analysis of the 80 articles published last year, this time frame has narrowed. Depending on factors such as the way and strength of cannabis consumption, the user can remain impaired for between 3 and 10 hours.
This information can help inform patient counseling, help recreational users make better decisions about performing tasks such as driving after consuming cannabis, and help update laws to better reflect the reality of cannabis harm.
Psychopharmacologist Iain McGregor from the University of Sydney (USYD) in Australia: “THC can be detected in the body weeks after consuming cannabis, while it is clear that the damage is much shorter. he explained in 2021.
“Our legal framework probably needs to catch up and focus, as with alcohol, on the period when users pose a greater risk to themselves and others. Prosecuting based solely on the presence of THC in blood or saliva is patently unfair. .”
Meta-analysis is what it sounds like: reviewing and analyzing the relevant scientific literature, cross-referencing the results to arrive at a conclusion based on a wider methodology and subject (in this case, humans) than can be covered. in a single study.
For this research, a team led by USYD nutritionist Danielle McCartney referenced 80 separate studies examining the effects of tetrahydrocannabinol (THC), the intoxicating compound in cannabis, and conducted the first such meta-analysis.
From those 80 papers, the team looked at 1,534 “performance outcomes” from people who used cannabis; that is, how these people performed on driving or equivalent cognitive tasks at different stages after taking cannabis.
The duration of the impairment depended on three main factors: how strong the THC dose was; whether the cannabis was inhaled or taken orally, in the form of food, capsules or drops; and whether the person was an occasional or regular cannabis user.
“According to our analysis, impairment can last up to 10 hours when high doses of THC are consumed orally. However, the more typical duration of impairment is four hours when lower doses of THC are consumed through smoking or vaping and simpler tasks are performed.” McCartney said.
“This impairment may extend to six to seven hours when higher doses of THC are inhaled and complex tasks such as driving are assessed.”
Interestingly, regular cannabis users can build up tolerance and perform better on cognitive tasks than occasional users after consuming the same amount. Therefore, it is not easy to predict how long or how long cannabis will harm a regular user, as they may need to take larger doses to reach levels of intoxication similar to occasional users.
“We found that impairment is more predictable in occasional cannabis users than in regular cannabis users.” explained Thomas Arkell, behavioral pharmacologist at USYD.
“Heavy users show significant tolerance to the effects of cannabis on driving and cognitive function, while generally showing some impairment.”
The results suggest that most driving-related skills can return within five hours of inhaling cannabis, although this time can vary.
More research needs to be done on these time intervals for regular users to better characterize the overall effects of THC. But once it did, the information could guide legislation, the researchers said.
“Laws should be about road safety, not arbitrary punishment” McGregor said. With cannabis legal in more and more jurisdictions, we need an evidence-based approach to drug-driving legislation.”
The research was published in Neuroscience & Biobehavioral Reviews.
An earlier version of this article was published in April 2021.