Driving under the influence of illicit substances has always been illegal in Maryland, but with marijuana recently decriminalized, driving while high has become more frequent according to data from the state – and potentially harder to catch.
In 2023, after the legalization of marijuana in July, reports of driving under the influence of cannabis (DUIC) spiked by more than 20%, according to the Maryland Cannabis Administration’s 2024 Maryland Medical Cannabis Patient Survey. The administration defined DUIC as driving while consuming or within three hours of consuming cannabis. Last year those reports leveled out with a 5% drop in respondents who said they had driven under the influence at least once in the month before the survey.
According to the MCA’s 2025 Maryland Cannabis Use Biannual Study, drug-impaired driving arrests have dropped over 70% in the past seven years – not specifying arrests due to cannabis impairment. However, cannabis-positive DRE evaluations accounted for about 25% of all evaluations in 2023 according to the study.
Unlike other states that have zero-tolerance or legal limit laws – Maryland has no state law specifying how long drivers should wait before getting behind the wheel nor any legal threshold for acceptable THC levels. The MCA’s resources point to a 2017 study suggesting drivers should wait at least six hours after consumption due to potential delayed effects and impairment.
There are currently no cannabis breathalyzer tests like those available for alcohol screening. Efforts to create a breathalyzer have largely failed, because “the THC molecule is much bigger than ethanol and its behavior after ingestion is very different from alcohol,” Dr. Guohua Li, professor of epidemiology and the founding director of the Center for Injury Science and Prevention at Columbia University, said in an interview with The Journalist’s Resource.
Generally, blood and saliva tests are used to measure THC levels. According to the MCA’s biannual study, those tests can produce false positive results since THC can stay in the body for weeks – long after intoxicating effects dissipate.
The only roadside test for cannabis that has been released to date is SoToxa, a portable saliva testing device released in 2019 and tested in pilot programs in Michigan and Indiana. Maryland relies on Drug Recognition Expert (DRE) police officers to assess drivers’ impairment behind the wheel.
“Marijuana is very different from alcohol in important ways,” said Li, who has published several studies on marijuana and driving. “The effect of marijuana on cognitive functions and behaviors is much more unpredictable than alcohol. In general, alcohol is a depressant drug. But marijuana could act on the central nervous system as a depressant, a stimulant, and a hallucinogenic substance.”
According to Dr. Timothy Kerns, the director of the Maryland Department of Transportation Motor Vehicle Administration’s Highway Safety Office, DRE officers are trained to identify drug use and can identify seven different classifications of drugs – including both stimulants and depressants.
“If an arrest is made or somebody’s pulled over with a suspicion of impaired driving, and the alcohol test is negative, then they can ask a DRE to come to the scene and they will conduct a separate set of roadside testing so they can try to determine if that individual might be under the influence of a certain type of drug,” said Kerns.
Kerns estimates about 170 DRE certified officers in the state – with the more populated areas having more than other jurisdictions. Kerns says the Highway Safety Office supports different agencies that can do roadside tests if DREs aren’t available. Otherwise, officers rely on field tests and body cam footage to charge drivers.
According to the MCA’s biannual study, some Maryland judges don’t qualify DRE testimony as expert testimony. So there are times that the initial officers’ typical field sobriety tests, like walking a straight line, and body cam footage are all they have to justify a DUI charge.
“It’s challenging at times, but the Highway Safety Office has a judicial outreach liaison that we’re hoping will be able to provide some education because there is some case law related to a DRE that’s kind of what they’re basing their decisions on. So we’re just trying to educate folks, the prosecutors and the judiciary, as much as we can on what best practices are for law enforcement, the DRE program and what it does, and what it can identify and determine,” said Kerns.