As cannabis becomes decriminalized or legalized for recreational or medical use in Missouri and many other states, questions have been raised about driving under the influence of marijuana. Drunk driving charges in Missouri are based on blood alcohol concentration, or BAC, and the legal limit of 0.08 was established after lengthy studies examining the effect of alcohol on driving. It is relatively easy for police to test BAC without invasive devices by making use of roadside or in-station breath tests. The driver blows into the device, which measures BAC through assessing alcohol in the breath. While the breath test is now standard and widely accepted, it was initially controversial and heavily disputed.

However, no similar test exists for cannabis. Drivers are accused of driving under the influence of cannabis and face DWI charges in court, bearing the same hefty penalties as a drunk driving conviction. At the same time, there is little clear scientific evidence to indicate how cannabis use influences driving behavior or how much cannabis could impair a driver’s decision-making and judgment. In addition, blood and urine tests used to detect cannabis may pick up compounds that are days old with no impact on driving ability. An attorney is essential to help sift through the information and determine what is credible what is junk science. 

As a result, scientists have been exploring the creation of a breath test for cannabis. One device was announced by the University of Pittsburgh. However, while the machine can measure THC, the psychoactive compound in cannabis, in the breath, it is not clear how that relates to a person’s level of intoxication. There is little information about how THC breath results correlate with driving impairment.

People charged with DWI for cannabis use may face the loss of their driver’s license as well as heavy fines or jail time. A DWI defense attorney may work with people to challenge police allegations and aim to protect their rights.