With the growing number of low odor strains on the market and it being harder to detect whether someone is high, how long a cannabis high lasts can be very subjective. It is, however, an important matter when considering drug-driving laws which can penalize people for the presence of tetrahydrocannabinol (THC), a psychoactive substance in cannabis, in their system. As such, to facilitate public policy decisions, researchers have published a new study that may help determine how long the average 'high' lasts.
"THC can be detected in the body weeks after cannabis consumption while it is clear that impairment lasts for a much shorter period of time," says Iain McGregor, one of the authors of the paper.
"Our legal frameworks probably need to catch up with that and, as with alcohol, focus on the interval when users are more of a risk to themselves and others. Prosecution solely on the basis of the presence of THC in blood or saliva is manifestly unjust."
For the study, the researchers conducted a meta-analysis of 80 papers focused on cognitive impairment after consuming THC. The papers included data from 1,534 'performance outcomes' taken at various points while participants drove or completed comparable cognitive tasks after consuming cannabis.
Ultimately, the researchers found that how long the impairment lasted depended on three factors: the strength of the THC consumed; whether cannabis was inhaled or orally ingested as food; and how often the participants used cannabis. In particular, the researchers found that if orally consumed at high doses, cannabis could lead to impairment lasting up to 10 hours.
Meanwhile, if consumed at lower doses via smoking or vaping, the effects could last for a more typical four hours. They also found that the kind of tasks performed also influenced how long impairment lasted. For simpler tasks, impairment seemed less significant, lasting for just four hours when inhaled. However, after inhaling higher doses of THC, participants could be impaired for up to six or seven hours while carrying out more complex tasks like driving.
The researchers noted, however, that regular users of cannabis tended to perform better on cognitive tasks than occasional users consuming the same amount due to a build-up of tolerance. As such, they say it is not easy to predict how much cannabis would significantly impair a user and for how long its effects would be present. This is especially true for more regular users.
Nevertheless, the researchers say that their findings suggest that most driving-related skills may return within 5 hours of inhaling cannabis. However, they did warn that more research is needed to assess time intervals for regular users to better understand how THC affects people on a broader basis.