A team of researchers led by Dr. Marilyn Huestis from the Biomedical Research Center, National Institutes of Health, has investigated the effects of combining alcohol and cannabis. The findings show that when compared to cannabis use alone, a combination of cannabis use with alcohol consumption leads to higher blood concentrations of the psychoactive tetrahydrocannabinol (THC), along with THC’s primary active metabolite, 11-hydroxy-THC (11-OH-THC).

THC, the active ingredient of cannabis and marijuana, is ranked second after alcohol, as the substance present in the blood of impaired drivers, fatally injured drivers, and crash victims. The Centers for Disease Control and Prevention (CDC) reports that nearly one third (31%) of all traffic-related deaths involve alcohol. According to the US National Institute on Drug Abuse (NIDA), 4-14% of drivers who got injured or died in accidents tested positive for THC.

Cannabis and alcohol turn out to be the most common combination in accidents involving automobiles, according to the US National Highway Traffic Safety Administration (NHTSA). However, the effect of one drug on the other has not been studied thus far, and this is the gap the current study aims to fill.

In the study, a group of 32 adults, who were cannabis smokers, drank placebo or low-dose alcohol 10 minutes before inhaling placebo, low- or high-dose of THC containing vaporized cannabis. Blood and plasma were obtained from the participants before and after (8.3 hours) ingestion. There were a total of 6 combinations each participant was required to complete.

The results tabulated from data collected from 19 participants who completed all sessions showed:

• The amount of THC detected in participants with low dose of alcohol was significantly higher than without alcohol.
• Similarly, 11-OH-THC levels were also significantly increased when a low level of alcohol was present in the system. 

The lead author of the study, Marilyn A. Huestis, PhD, said in the Press release of the American Association for Clinical Chemistry, “The significantly higher blood THC and 11-OH-THC [median maximum concentration] values with alcohol possibly explain increased performance impairment observed from cannabis-alcohol combinations,” said. “Our results will help facilitate forensic interpretation and inform the debate on drugged driving legislation.”

Written by Mangala Sarkar Ph.D.