How Does Marijuana Testing for a DUI Work?

Any time we hear “DUI” we immediately think alcohol. But marijuana-related DUI arrests are happening with more and more frequency. Although Florida’s proposed medical marijuana initiative failed narrowly last year it will be brought up again in the next election cycle. Colorado has legalized recreational marijuana use, and many states seem to be following on its heels.

More widespread use of marijuana will lead to more marijuana DUI arrests. But, unlike in alcohol DUI’s, Florida does not have a “breathalyzer” for marijuana. Several companies are working to develop testing devices to fill this gap.

Right now Florida primarily uses urine samples to test for the presence of drugs in drivers arrested for a DUI. The samples have to be sent to the Florida Department of Law Enforcement for testing to determine the presence of marijuana. But while proving that the defendant had marijuana in their system may be simple, proving that the defendant was driving while impaired by marijuana is much more complicated.

Florida Judge Karl Grube, who routinely lectures on DUI law, has called Florida’s statute the “hard way” for the prosecution to prove its case. Florida’s statute requires the prosecution to prove that the defendant:

  1. Was driving a car;
  2. While under the influence of a controlled substance; and
  3. The controlled substance caused impairment of the defendant’s normal faculties.

It’s not enough that the defendant had marijuana in their system at the time they were driving, the prosecutor has to prove that the marijuana cause them to be impaired. If the prosecution cannot prove this beyond and to the exclusion of every reasonable doubt, the defendant cannot be convicted of a DUI.

Other states handle this in different ways. Some states set a limit for drug concentration, the same way Florida has the .08 or above presumption of impairment. If a test sample comes back with a higher concentration than the legal limit, then the driver is presumed to be impaired. Montana and Washington, for example, have a THC concentration limit of 5 nanograms per milliliter, while Pennsylvania has a limit of 1 nanogram per milliliter.

Still other states have a “zero tolerance” law, where the defendant is presumed impaired if there is any controlled substances in their system. The problem with this system is that many drivers could have marijuana in their system and not be impaired at all, and they would lose the safeguard of the state having to prove they were impaired to prove a DUI.

Requiring the prosecutor to prove impairment is the most fair and equitable way for the law to work. Yes, it makes the job of the prosecutor difficult, but that’s the way our laws protect our rights.