Researchers at Johns Hopkins Medicine found that combining cannabis edibles with alcohol causes significantly greater driving impairment than using either substance alone [1].
This finding suggests a critical gap in public safety, as the resulting impairment may not be detectable through the standard roadside tests used by law enforcement to identify intoxicated drivers [3].
The study, funded by the National Institute on Drug Abuse (NIDA), focused on how these substances interact to affect motor skills and cognitive function [1]. Researchers in Baltimore, Maryland, examined whether existing field sobriety tests could accurately capture the level of impairment caused by the combination [2].
According to the research, consuming a cannabis brownie along with two or three alcoholic drinks [1] produced impairment levels greater than those seen in individuals who were legally drunk on alcohol alone [4]. This synergy creates a high-risk scenario for motorists who may believe they are within safe limits based on their alcohol consumption.
Despite the increased danger, the study revealed that standard field sobriety tests often fail to detect the specific impairment related to cannabis [1]. This means a driver could be significantly impaired by the combination of an edible and alcohol but still pass the physical tests typically administered by police officers [3].
The results highlight a disconnect between the physical ability to operate a vehicle and the diagnostic tools currently available to authorities [2]. While alcohol is easily measured via breathalyzers, the delayed onset and metabolic processing of edibles create a different profile of impairment that does not always align with traditional sobriety markers [1].
“Combining cannabis edibles with alcohol causes far greater driving impairment than either substance alone.”
The study indicates that current law enforcement protocols for detecting impaired driving are insufficient for the modern landscape of legal cannabis use. Because the combination of edibles and alcohol bypasses standard sobriety checks while increasing actual impairment, there is a heightened risk of undetected dangerous drivers on U.S. roads, potentially necessitating new diagnostic tools for roadside testing.
