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Driving and Marijuana Interactions—Why Is It So Complicated?

Almost everyone is aware of the dangers of drunk driving. Hundreds, if not thousands, of studies, have examined the cause-and-effect of drinking on driving ability. A standardized .08 percent blood alcohol content (BAC) has been set across states as a safe limit. Breathalyzers can accurately assess BAC quickly on the location of a pulled-over driver. None of this, however, is true for marijuana. Here are a few reasons why assessing the relationship between marijuana consumption and driving is so complicated.

Different Compounds, Different Effects

There are over 500 compounds unique to marijuana. Tetrahydrocannabinol (THC) is the best-known compound in marijuana responsible for the “high”. Most drug tests look for this specific compound, but many more of these 500 compounds could potentially cause impairment related to driving ability. Another problem is that some cannabis products which produce no noticeable psychoactive effects, and certainly not enough to impair driving, can sometimes contain trace amounts of THC which might indicate the presence of marijuana in the system even though there is no reduced capacity to drive safely.

Defining Intoxication Levels

As mentioned earlier, clear and uniform limits on alcohol content in the blood for an individual driver make following drunk driving laws simple. On the other hand, no such universal standard exists for enforcing marijuana driving laws. While all states have laws against driving while impaired by marijuana, what constitutes being impaired remains unclear. One of the reasons for the lack of a set allowable limit for marijuana is the lack of scientific research. While marijuana remained illegal until the legalization revolution in the 21st century, there was a limited amount of research conducted on safe limits. Analyzing marijuana impairment to create laws that make sense is lagging behind the widespread availability of the drug in states where it’s now legal.

Accurate Testing Challenges

Previously, a field sobriety test similar to the one conducted for alcohol, or a urine or blood test performed at the station, were the only ways to legally establish impairment from marijuana. Unfortunately, the field sobriety test is not totally accurate. The only accurate option, a blood or urine test at the station, is time-consuming and poses important constitutional protection questions regarding the 4th amendment right of citizens. More accurate tools are currently being developed for roadside testing.

As legalization trends continue, laws will become clearer and testing will become more convenient. For the time being, driving high without knowing your level of intoxication could cause prolonged and complicated interactions with law enforcement.


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