If you ask 50 different people how long the effects of cannabis last, you will probably get 50 different answers. This can be a problem in finding out how long a patient who is using the medicine for medical purposes will remain affected.
A new meta-analysis of 80 papers reduced this time. Depending on factors such as how cannabis is consumed and how strong it is, the user may be affected for three to 10 hours.
This information can help inform counseling information to patients, help recreational users make better decisions about tasks such as driving after cannabis use, and help update laws to better reflect the reality of cannabis use.
“THC can be detected in the body weeks after cannabis use, while it is clear that the damage lasts for a much shorter period of time,” said psychopharmacologist Iain McGregor of the University of Sydney (USYD) in Australia.
“Our legal frameworks probably need to catch up and, as with alcohol, focus on the extent to which users are at greater risk to themselves and others. Processing only on the basis of the presence of THC in the blood or saliva is obviously unfair. . “
A meta-analysis is what it sounds like: a review and analysis of the relevant scientific literature, crossing the results to arrive at a finding based on a wider range of methodologies and topics (in this case, people) than can be covered in a single study.
For this research, a team led by USYD nutritionist Danielle McCartney referred to 80 separate studies on the damage of tetrahydrocannabinol (THC), the intoxicating compound in cannabis, performing the first meta-analysis of this kind.
Of the 80 papers, the team studied 1,534 “performance results” from people who took cannabis; that is, how these people behaved in driving or equivalent cognitive tasks at different stages after taking cannabis.
How long the damage lasted depended on three main factors: how strong the dose of THC is; if cannabis has been inhaled or administered orally in the form of food, capsules or drops; and whether the person was an occasional or regular cannabis user.
“Our analysis indicates that the damage can last up to 10 hours if high doses of THC are consumed orally. However, a more common duration of damage is four hours, when lower doses of THC are consumed through smoking or vaporization and simpler tasks are undertaken. “McCartney said.
“This damage can last up to six or seven hours if higher doses of THC are inhaled and complex tasks, such as driving, are assessed.”
Interestingly, regular cannabis users can increase tolerance and behave better in cognitive tasks than occasional users after consuming the same amount. Therefore, it is not easy to predict how much cannabis will affect a regular user or for how long, as they may take higher doses to reach the same level of intoxication as an occasional user.
“We found that impairment is much more predictable in occasional cannabis users than regular cannabis users. Heavy users have significant tolerance to the effects of cannabis on driving and cognitive function, while they usually have some impairment,” said behavioral pharmacologist Thomas Arkell also from USyd.
The findings suggest that most driving skills may return within five hours of inhaling cannabis, although this time may vary.
More research will need to be done during these time intervals for regular users to better characterize the effects of THC everywhere. Once this is done, however, the information can guide the legislation, the researchers said.
“Laws should be about road safety, not arbitrary punishments. Given that cannabis is legal in an increasing number of jurisdictions, we need a evidence-based approach to drug trafficking laws.” said McGregor.
The research was published in Neurosciences and bio-behavioral reviews.