Getting high before getting into a car and driving, while the practice is not exactly commonplace is becoming more of a problem. This comes as researchers and anecdotal evidence finds that the widespread belief that recreational use of marijuana is harmless – it’s legal in four states and the District of Columbia – is quite a bit of hot air. The facts are that smoking pot, especially when combined with consumption of alcohol, is detrimental to safe driving.

It’s time to get these facts instilled in our minds so we can act accordingly. But what is the truth? How does marijuana serve to debilitate driving ability? Let’s take a look at what some of the experts have to say on the subject.

Number of “High” Drivers on the Increase

A report from Fox News quotes a statistic from the National Highway Traffic Safety Administration (NHTSA) that the number of drivers high on pot has shot up 50 percent since 2007. The report goes on to say that because humans metabolize marijuana differently, the job of setting a legal limit for pot is that much more difficult. It’s not as simple as declaring that 0.05 blood alcohol content (BAC) means anyone at that level or above is driving impaired. Until there’s a verifiable way to detect the levels of delta9-tetrahydrocannabinol (THC) and a standard to measure by, it’s pretty much a guessing game.

Some states use a numerical nanogram scale to measure the amount of THC. In Washington and Colorado, two states where recreational use of pot is now legal, the threshold for a DUI is 5 nanograms or more. In Illinois, a threshold of 15 nanograms of THC is being proposed by lawmakers.

According to, citing the NHTSA’s 2013-2014 National Roadside Survey, 12.6 percent of weekend night drivers tested positive for THC. In 2007, it was 8.6 percent.

How Pot Affects Driving Ability

What are the dangers of driving while high on marijuana? Is it the same as with alcohol? Is it better or worse than drinking and driving? Here the experts are somewhat divided, some saying pot use is less harmful than alcohol, while others saying it has potentially very dangerous risks.

In the Fox News report, toxicology expert Marilyn Huestis said that marijuana affects three important areas:

  • Divided attention
  • Executive function
  • Critical thinking

A 2009 study found that marijuana affects attentiveness, vigilance, perception of speed and time, and use of acquired knowledge. With respect to driving while high on pot, the study authors said it results in driver impairment in every performance area related to safe driving, such as tracking, visual functions, motor coordination, and complex tasks that require divided attention. That same report said that marijuana, when combined with alcohol consumption, has “additive or even multiplicative effects on impairment.”

A study by Hartman in 2013 found that marijuana and alcohol used together made drivers more impaired, resulting in more lane weaving.

Another study on the co-use of alcohol and cannabis and its effect on driving by Meenakshi Subbaraman, PhD, associate scientist and biostatistician at the Alcohol Research Group in Emeryville, California found that the physical signs are not that different than just drinking or just smoking – heart rates and dilated pupils, and also subjective measures like self-reported intoxication. Ms. Subbaraman said that the findings from the study will help clinicians and prevention/treatment specialists advise patients and others in the community regarding the elevated risk of consequences related to simultaneous use. “I also hope that as the cannabis industry continues to grow, manufacturers will consider some sort of warning label related to increased risks when mixing alcohol and cannabis,” she said.

The National Institutes of Health (NIH) says that marijuana is the drug that is most often found in the blood of drivers who have been involved in accidents, including fatal accidents. The NIH also says that the risk of becoming involved in an accident “roughly doubles” with marijuana use, according to a meta-analysis of several studies.

What Are the Other Dangers of Marijuana Use?

The National Institute on Drug Abuse (NIDA) says marijuana is a “mind-altering chemical” that can be addictive. Furthermore, the potency of THC has been increasing over the years and today is causing much more harmful effects in users. Use of marijuana can bring about numerous physical and mental effects, including:

  • Breathing problems – similar to those experienced by tobacco smokers, including increased phlegm, difficulties breathing, lung infections, etc.
  • Increased heart rate – which lasts for up to 3 hours after smoking, and may increase the risk of having a heart attack
  • Problems with child development during and after pregnancy – with children potentially having problems with attention, memory, and solving problems

Long-term marijuana use has been linked with temporary hallucinations and paranoia, worsening symptoms in those diagnosed with a severe mental illness, such as schizophrenia, depression, anxiety, and suicidal thoughts in teens.

Breathalyzer for Pot

While there is no currently approved breathalyzer to detect the amount of THC in a person’s system, A Canadian company, Cannabix Technologies, Inc., is developing a hand-held marijuana breathalyzer that could soon be used in the workplace and with law enforcement. The project is currently in the prototype stage.

This can’t come soon enough, according to those who worry about increasing numbers of drivers on the road who toke before getting behind the wheel. Just last week, Delaware decriminalized the possession and use of a small amount of marijuana (up to an ounce), although driving under the influence of pot is still criminal, as is possession and use by anyone under the age of 21.

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