Combining cannabis edibles with alcohol can impair driving significantly more than using either substance alone, according to new research from Johns Hopkins Medicine. The study also found that standard field sobriety tests often failed to detect impairment caused by cannabis, whether used by itself or with alcohol. These findings highlight the risks of mixing cannabis and alcohol.
The study, published in *JAMA Network*, involved healthy adults aged 21 to 55. Participants received either a cannabis brownie containing tetrahydrocannabinol (THC) or a placebo brownie. They also consumed an alcoholic beverage or a placebo drink. Alcohol doses were adjusted to achieve breath alcohol concentrations of 0.05% or 0.08%.
Researchers observed that combining cannabis edibles with alcohol resulted in more severe and prolonged driving impairment. Participants also reported feeling more intoxicated when they used both substances together. However, standard field sobriety tests only identified significant intoxication when alcohol levels reached 0.08% breath alcohol concentration (BrAC).
Cannabis-related impairment often went undetected by these tests. The study's lead author, Austin Zamarripa, Ph.D., stated that the interaction between cannabis edibles and alcohol may be synergistic, not merely additive, in producing impairment. This has important implications for real-world risk.
Tory Spindle, Ph.D., the study's principal investigator, noted that this is the first controlled study to examine the interaction of cannabis edibles and alcohol. He emphasized that consuming typical doses of cannabis edibles with even low doses of alcohol can produce driving impairment comparable to or greater than alcohol alone at the legal limit. As cannabis legalization expands, public health officials and policymakers need to address these risks.
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