In the debate over cannabis legalization, one of the most common arguments in opposition revolves around fears about stoned driving.
Unlike with alcohol, it’s still basically impossible to quantify just how stoned someone is — that is, there’s no good technology to determine whether any certain amount of THC in your system is enough to be considered a standard amount for impairment.
When it comes to cannabis, impairment is highly contingent on your own tolerance, when you consumed cannabis, what you consumed, how you consumed it, and any other number of factors. It’s also important to note that the mere presence of THC, the main psychoactive compound in cannabis, in your system is not necessarily indicative that you’d be too high too drive, or that you’d even be that high at all.
The issue isn’t necessarily measuring the quantity of cannabinoids in a person’s blood, urine, saliva, or hair, but how to interpret the results of any cannabis drug test.
Unlike alcohol, which is water soluble, THC is fat soluble, meaning it can linger in the body for days, weeks, or even months after use — depending on how heavily you consume. But while THC remains in your body for a while, that’s also far from indicative of how it’s affecting you. That means you can fail a drug test, even if you are sober and have been sober for days.
All this taken into account, scientists still have not been able to come up with technology that accurately measures how THC affects your body in real time, and whether that effect has you impaired.
Nonetheless, while the impairment measurement technology leaves something to be desired, you can still get a DUI for marijuana. If you are going to smoke and drive, it’s recommended to wait at least six hours so as to ensure at least that you are not high when you get behind the wheel.