Does smoking weed affect driving? It’s complicated | Health

As Germany moves closer to legalizing marijuana, politicians, doctors and lawyers will need to reach some sort of agreement on how much a person can legally smoke before driving. Alcohol consumption limits before driving – people’s blood alcohol level must be below 0.05% in Germany and below 0.08% in the United States – have been the subject of much research. But with few case studies to work from, it’s hard to say how much cannabis someone should be allowed to consume before driving a vehicle.



A team of researchers from universities across Germany conducted a systematic review of studies on cannabis use and car accidents in 2021 to try to assess this risk.

They found that the studies overall indicated a small, but significant, risk of car crashes after people used marijuana. While some studies have shown a significant correlation between high blood levels of THC and crashes, most have not supported the correlation at lower levels.

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THC stands for delta-9-tetrahydrocannabinol, the main psychoactive ingredient in marijuana. It makes marijuana users feel high.

Ultimately, the German researchers could not come up with a clear threshold to recommend implementation into law, such as the 0.05% for alcohol.



THC levels difficult to measure

Another problem: THC levels in the blood are more difficult to measure than alcohol levels. While the alcohol wears off in a few hours, the THC stays around longer, making it hard to tell if someone was high while driving or just got high the night before.

“It can be difficult to know whether cannabis use is occasional or frequent, or when the last cannabis use was before the accident,” the study authors wrote.

This is a significant challenge for researchers because the effects of smoking weed typically peak after 30 minutes and wear off after four hours, the researchers wrote. So if a person has a crash 12 hours after smoking weed, you can’t point to drugs as the obvious cause of the crash.



In many US states and Canada, blood THC limits have been set at 2 or 5 nanograms per milliliter, or ng/ml, for drivers. Many European countries have a limit of 1 ng/ml.

But some have criticized Europe’s limits because they may not indicate impairment in people who smoke weed very frequently and have developed a tolerance to the drug.

“Due to the accumulation of cannabinoids in fat, some daily users may have blood THC [levels that are higher than] 1 ng/ml after a week or more of abstinence,” the authors wrote.

Have you smoked a joint or eaten a weed cookie?

Variability in weed peaks based on consumption can also complicate results. When a person gets high after use depends on how they use the drug. If a person smokes weed, they can expect to get high within minutes. But if they’re eating weed in edible form — a brownie, say — they may not feel high until an hour after consuming the edible.



And because recreational marijuana use is illegal in Germany and the weed is not sold in regulated quantities, it’s impossible for users to know how much they’ve smoked. One joint can contain a lot more – or a lot less – weed than another.

Smoking marijuana can affect your driving

According to a 2021 study titled “Cannabis and Driving” by a Yale researcher, the most conclusive way to study the impact of cannabis on people’s driving skills would be to have them consume some of it and then have them drive a car on a normal road. Godfrey Pearlson.

This is obviously not possible for ethical reasons, so researchers must content themselves with measuring the effect in simulated situations. While these studies may offer some insight, they do not perfectly simulate real-world traffic conditions.



In general, researchers have found that cannabis can impact people’s concentration and attention on the road, and also has a significant impact on a person’s ability to weave between other cars in traffic. . People’s reaction times were generally unimpaired, and drivers didn’t seem more likely to drive faster than normal.

Overall, impairment was generally higher while driving after consuming alcohol. This was also confirmed by a French study that followed fatal accidents for two years.

They found that drivers under the influence of alcohol were 17.8 times more likely to be responsible for a fatal crash, while drivers under the influence of cannabis increased their risk of a crash by 1.65 times. be responsible for a fatal accident.

Studies in the United States also found that accidents related to marijuana use were more common in states where the substance was legalized, suggesting that the acceptability of the drug drove people to take it. less seriously.