• States which legalised medical cannabis saw “traffic fatalities by 9%”
  • Legalising medical cannabis is also associated with “decreased beer sales”
  • One study even found that “low concentrations of THC do not increase the rate of accidents, and may even decrease them”

One of the leading arguments against legalising cannabis, even for medicinal use, is that it will lead to an increase in traffic accidents due to an increase in stoned drivers.

While there is evidence that driving under the influence of THC impairs certain driving functions, several studies are now questioning whether legalising cannabis has any valid links to an increase in fatal road traffic accidents.

Researchers at the University of Colorado-Denver looked into traffic accident fatalities in 16 states which had legalised access to medical cannabis, surprisingly finding that these states actually saw a decrease in traffic deaths.

Using data from the National Survey on Drug Use and Health (NSDUH) from 1990-2009, researchers found that states which legalise medical cannabis see “traffic fatalities fall by nearly 9%.”

“We went into our research expecting the opposite effect,” explained Daniel Rees, study co-author.

This is not to suggest that cannabis makes you a better driver.

Researchers believe that the main reason MMJ (medical marijuana) states see a reduction in fatal traffic accidents is because cannabis can act as an effective substitute for alcohol.

According to the study, legalising medical cannabis “leads to a decrease in alcohol consumption,” especially among those aged 20-29, and there is also an “associated with decreased beer sales, the most popular alcoholic beverage among young adults.”

The study also found that while legalisation does lead to an increase of consumption among adults, there was “no evidence that the use of marijuana by minors increased,” challenging another common argument used against legalising cannabis.

Due to this substitution of alcohol for cannabis, in states which legalised medical cannabis, researchers found an associated with a 6.4% decrease in fatal crashes that did not involve alcohol, as well as an almost 12% decrease in any-BAC (Blood Alcohol Concentration) fatal crashes per 100,000 licensed drivers.

Despite several trials arguing that driving while under the influence of cannabis increases crash numbers and reduces drivers’ ability, researchers at Yale claim these studies are “inconsistent,” neglecting to take into account other control factors, such as “risky driver behaviours and unsafe driver attitudes.”

They even suggest that “low concentrations of THC do not increase the rate of accidents, and may even decrease them,” but higher doses of cannabis, for example, serum concentrations of THC higher than 5 ng/mL, are associated with an increased risk of accidents.

However, they also found evidence that suggests experienced cannabis users can drive safely under higher doses of THC than those less experienced due to a tolerance build-up to the effects of THC.

Experienced users, due to an increased awareness that they are impaired, also tend to compensate effectively for their impairment by utilising a variety of behavioural strategies such as “driving more slowly, passing less, and leaving more space between themselves and cars in front of them.”

The researchers questioned whether this improved performance of driving while high by experienced users is because of either this physiological tolerance or due to these developed behavioural strategies and whether they can be taught to new or infrequent medical cannabis patients.

Researchers at the University of Massachusetts Medical School also found no evidence to suggest that use of cannabis impairs driving ability.

Reviewing current literature regarding cannabis as it relates to driving performance and traffic safety, researchers found “no studies to our knowledge that associate the medical use of marijuana with driving impairment.”

However, it has to be remembered that THC does have an impact on a driver’s ability to perform certain tasks.

A study from researchers in the UK detailed how cannabis impaired participants driving skills, explaining why stoned drivers tend to drive slower.

Researchers found that there was a reduction of average speed on simulated motorway driving when participants had the high or low doses of cannabis, strongly suggesting that participants were “aware of their impairment, but attempt to compensate by driving more cautiously.”

However, they concluded that while drivers under the influence of cannabis tend to drive more cautiously,“In terms of road safety, it cannot be concluded that driving under the influence of cannabis is not a hazard, as the effects on various aspects of driver performance are unpredictable.”

Driving under the influence of THC clearly impacts users’ ability to drive, but this does not necessarily lead to an increase in traffic accidents.

Cannabis was legalised for medicinal use in the UK in November 2018. Even though there is still a very limited number of patients who have been able to get a prescription, the number of patients using medical cannabis is destined to rapidly increase over the coming years.

Policies will need to be written to accommodate an inevitable corresponding increase in medical cannabis patients driving while under the influence of their medication.

Simply banning any amount of cannabis allowed in a drivers’ bloodstream is clearly not a suitable position to take. There is not enough convincing evidence that it impairs drivers enough for them to cause a fatal traffic accident, and a total ban would limit the quality of life of medical cannabis patients, potentially leaving them house-bound.

As a users’ tolerance to THC increases so does their ability to drive safely while under the influence, but there still remains a risk they could cause an accident.

Until more research is conducted into the exact impact of cannabis on driving, the study from Yale concludes that “patients who smoke cannabis should be counselled to wait several hours before driving.”

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