Many marijuana users assume that it is safe to drive just a couple of hours after getting high.
But the drug, which is legal in 38 states, affects alcohol differently and can stay in the body longer, making it difficult to know when you can get behind the wheel with minimal risk.
Researchers at the University of California, San Diego have now warned that You should wait at least four hours before driving after smoking a joint and at least eight hours after eating a cannabis edible.
However, guidelines published in 2022 in the International Journal of Drug Policy said inhaling marijuana can impair driving skills for six to eight hours, and edibles can impair judgment for up to 12 hours.
This is because edibles are typically stronger than joints and take longer to enter the bloodstream, meaning they take longer to reach the “peak” of the high.
Marijuana affects you differently than alcohol and can stay in your body longer, making it difficult to know when it’s safe to get behind the wheel.
The liver also converts ingested THC (the psychoactive component of marijuana) into a stronger form.
The warnings come after a significant increase in the percentage of deaths in car accidents related to marijuana.
The figure skyrocketed from nine percent in 2000 to 22 percent in 2018, according to a 2021 American Journal of Public Health study.
With alcohol, there’s a “one hour” rule, meaning for every drink you have, you should wait one hour before driving, according to the National Highway Traffic Safety Administration.
In the United States, for people over 21 years of age, driving with a blood alcohol concentration of 0.08 percent or more is illegal.
When you drink alcohol, the metabolization process is mainly done by the liver.
On average, a person will metabolize the equivalent of one alcoholic drink per hour, although this can vary depending on the person’s weight, height, gender, and body composition.
THC, on the other hand, is gradually released into the bloodstream, so it can remain in the body up to weeks later.
Marijuana is legal for recreational use in two dozen states and for medicinal purposes in 38.
Tetrahydrocannabinol, also known as THC, the part of the cannabis plant that makes you high, affects driving in multiple ways.
The percentage of deaths in car crashes involving marijuana skyrocketed from nine percent in 2000 to 22 percent in 2018, according to a 2021 American Journal of Public Health study.
People under the influence of marijuana tend to drive more slowly and their ability to stay in a lane, react quickly to a situation, and keep distance between cars is impaired.
It also reduces people’s ability to focus on more than one thing at a time, such as looking between the road, the mirrors and the speedometer.
Laws regarding how much marijuana can be in your system while driving differ by state.
Twelve states have zero-tolerance laws for any amount of THC, while others have a limit of between two and five nanograms per millimeter of blood.
The map above shows states that have and have not legalized cannabis.
A 2022 study published in the journal JAMA Psychiatry asked nearly 200 cannabis users to smoke THC or a placebo.
They then compared their driving in a simulator.
Between 45 and 50 percent of people in the THC group were categorized as having driving problems compared to the placebo group.
The researchers also asked the participants if they thought they were OK to drive.
Thirty minutes after smoking, about half of the participants were hesitant.
After an hour and a half, they said the effects were wearing off and they were more likely to drive.
But their driving performance was no better after 90 minutes than it was at 30 minutes after the crossing.
Tom Marcotte, co-director of the Medical Cannabis Research Center at the University of California, San Diego, who led the trial, said: “Even people who are very conscientious and say, ‘I’m not going to drive, I’m not going to drive.’ I’m too high,” I’m starting to think the effect is wearing off.
“At least according to our analysis, they still have problems.”
Overall, most participants began to show improvements from the impact of THC after three and a half hours, and returned to their normal state four and a half hours later.
In 2022, a 16-year-old girl with cannabis in her system died along with five teenage friends after failing to yield to an oncoming truck.
And in 2017, a 55-year-old New Jersey grandmother was found to be “high on marijuana” when she crashed and killed her two grandchildren, ages two and five, on the way home from a funeral.