Many marijuana users assume that they can drive safely just a few hours after getting high.
But the drug — which is legal in 38 states — affects you differently than alcohol and can stay in your body longer, making it difficult to know when you can get behind the wheel with minimal risk.
Researchers from the University of California, San Diego, have now warned about this After smoking a joint, you should wait at least four hours before driving, and at least eight hours after eating edible cannabis.
However, guidelines published in 2022 in the International Journal of Drug Policy say inhaling marijuana can alter driving ability for between six and eight hours, and edibles can impair judgment for up to 12 hours.
This is because edibles are often stronger than joints and take longer to enter the bloodstream, meaning it takes 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 in cannabis – into a stronger form.
The warnings come after a significant increase in the rate of fatal car crashes involving marijuana.
This figure shot up from nine percent in 2000 to 22 percent in 2018, according to a 2021 study in the American Journal of Public Health.
Alcohol has a “one hour” rule, meaning you should wait an hour for each drink you drink before driving, according to the National Highway Traffic Safety Administration.
In America, driving with a blood alcohol content of 0.08 percent or more is illegal for people aged 21 and over.
When you drink alcohol, the metabolization process occurs mainly through your liver.
On average, a person will metabolize the equivalent of one alcoholic drink per hour, although this can vary depending on a person’s weight, height, gender and body composition.
THC, on the other hand, enters the bloodstream gradually, so it can remain in your body for weeks afterwards.
Marijuana is legal for recreational use in two dozen states and medical in 38.
Tetrahydrocannabinol, also known as THC – the part of the cannabis plant that makes you feel high – affects driving in several ways.
The percentage of fatal car crashes involving marijuana skyrocketed from nine percent in 2000 to 22 percent in 2018, according to a 2021 study in the American Journal of Public Health.
People under the influence of marijuana tend to drive more slowly and their ability to stay in lane, react quickly to a situation and maintain distance between cars is altered.
It also reduces people’s ability to concentrate on more than one thing at a time, such as looking between the road, mirrors and speedometer.
Laws regarding the amount of marijuana that can be present in your system while driving vary from state to 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 the states that have and have not legalized cannabis
In a 2022 study published in the journal JAMA Psychiatry, nearly 200 cannabis users were asked to smoke THC or a placebo.
They then compared their driving behavior in a simulator.
Between 45 and 50 percent of people in the THC group were categorized as having impaired driving, compared to the placebo group.
The researchers also asked participants if they thought they were OK to drive.
Thirty minutes after smoking, about half of the participants hesitated.
After an hour and a half they said the effects were gone and that they started riding more often.
But their driving performance was no better after 90 minutes than 30 minutes after the joint.
Tom Marcotte, co-director of the Center for Medicinal Cannabis Research 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 too stoned'” , starting to believe it has worn off.
“In any case, in our analyzes they still have problems.”
Overall, most participants started showing improvements from the impact of THC after three and a half hours, and were back 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 New Jersey grandmother, 55, was found to be “high on marijuana” when she crashed on her way home from a funeral, killing her two grandchildren, ages two and five.