Stoner flicks notwithstanding and despite considerable public sentiment pushing for legalization of recreational marijuana, the complete facts about the effects of marijuana is still largely unknown. It’s even more problematic for certain age groups, such as adolescents and teens, and for drivers of vehicles or those operating dangerous equipment.  So how much THC (delta-9-tetrahydrocannabinol, the main chemical in marijuana) is too much to drive?

The answer is probably a lot less than most Americans think – whether they smoke it or not and get behind the wheel. Looking at the science and where the facts point – or don’t, here are a few things to keep in mind.

Marijuana’s Effects on Body and Mind 

Research continues on the effects of THC on body and mind by some of the most respected entities in the field. According to the National Institute on Drug Abuse (NIDA), THC is a mind-altering psychoactive chemical. Chronic use can lead to addiction. Research shows that about one in 11 users become addicted, while one in six teens that start using pot early will become addicted. Among daily pot users, the percentage skyrockets to 25 to 50 percent.

Cannabis has numerous short- and long-term effects on the human body and mind – none of which are innocuous, certainly not when the user gets behind the wheel of a vehicle and attempts to drive while high.

Short-term marijuana effects include:

  • Initial enhanced sensory perception and euphoria
  • Setting in of drowsiness and relaxation a short time later
  • Slowed reaction time
  • Problems with coordination and balance
  • Memory and learning problems
  • Increased heart rate and appetite
  • Anxiety
  • Hallucinations
  • Panic attacks
  • Psychosis
  • In combination with alcohol, marijuana increases heart rate and further slows mental processes and reaction time

On the other hand, long-term marijuana users face these possible health effects:

  • Chronic cough
  • Frequent respiratory problems
  • Mental health problems
  • In youths – possible loss of IQ points when marijuana use begins in adolescence
  • In pregnant women – possibility of babies born with memory and learning problems


Marijuana – In All Its Forms – Is Dangerous

The stereotypical marijuana user is depicted as smoking a joint. But there are other ways of using and consuming marijuana – some of which are even more dangerous than smoking it. That’s due to the concentrated amounts of THC and how quickly it gets to the brain.

According to various research studies, the potency of marijuana has increased tremendously over the years. Some media reports state that today’s marijuana is 30 times more potent than strains in the 1970s. But depending on how the sample was collected and analyzed, the strength of today’s marijuana – measured by THC levels – has increased between two and seven times since the 1970s. Translation: More potent pot means more dangerous pot.

Besides hand-rolled joints, marijuana can also be smoked in pipes or water pipes (called bongs), or in emptied cigars (blunts) that have been filled or partially filled with marijuana. Another way is to inhale vaporized fumes from marijuana.

Marijuana edibles have become popular as well. These include food laced with marijuana such as brownies, cookies, and candy and even brewed tea.

Smoking THC-rich resins from marijuana extracts is particularly dangerous due to the large amounts of THC delivered to users. Many such users end up in the hospital emergency room. The amount of THC inhaled through the practice called dabbing is about five times what a user gets from one puff of a marijuana joint. Dabbing uses forms of these extracts that include:

  • Honey or hash oil – generally a liquid that’s gooey in consistency
  • Wax or budder –with a texture that’s soft like lip balm
  • Shatter – this is an amber-colored hard solid

In addition, the butane (lighter fluid) that’s used to prepare these extracts often results in serious burns caused by fires and explosions.

What Happens Behind The Wheel To The Marijuana User? 

With the litany of negative effects of marijuana as background, what actually happens when a pot user gets behind the wheel and tries to drive? Here’s where it gets really scary.

The initial high marijuana users experience causes them to have an altered or distorted sense of time. Trying to gauge the time to stop a vehicle before a red light or to prevent rear-ending another vehicle could be seriously compromised.

Colors seem brighter and all visual perception is altered.

The marijuana-affected driver suffers a loss of coordination and balance, slowed reaction time – not able to react in time to avoid an accident, for example.

Sudden changes in mood are common, which can affect the driver’s ability to function behind the wheel.

Trying to determine a route, remembering directions, gauging whether the car in the adjacent lane is too close, attempting to determine speed and distance – all these essential driving functions are compromised by the presence of THC in the driver’s body.

The potential for paranoid thoughts, hearing and/or seeing things that aren’t there, thinking that someone is chasing you or that you’re in danger – these can all negatively affect your driving ability if you are under the influence of marijuana.

The NIDA warns that studies have found a direct correlation between the amount of THC in a driver’s blood “significantly” impairs driver’s capabilities. Furthermore, marijuana is the illicit drug most often found in drivers’ blood after car accidents, especially fatal ones. And marijuana can be detected in bodily fluids days and even weeks after acute intoxication. The risk of being involved in an automotive accident nearly doubles after marijuana use and drivers with THC in their blood are three to seven times more likely to be the cause of a vehicle accident than drivers without THC in their blood.

Add alcohol to the mix and the combination is potentially deadlier than with either drug on its own.

As for measuring the amount of THC in a driver’s blood, accuracy and reliability of devices still has a long way to go, as well as consistent laws across states.

Bottom line: How much THC is too much to drive? The answer is likely a lot less than anyone currently thinks.

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