In the most recent edition of the Diagnostic and Statistical Manual of Psychiatric Disorders, DSM-5™, the diagnostic criteria for alcohol use disorders have been simplified and improved. In prior editions of the DSM, alcohol use disorders were classified as either alcohol abuse or alcohol dependence. In DSM-5, alcohol use disorder (AUD) is considered to be a continuum based on the number of specific symptoms: the more symptoms, the more severe the disorder. This new classification system allows alcohol use disorder to be rated as mild, moderate, or severe. 

In a recent study published in JAMA Psychiatry, Bridget Grant and colleagues report on the one-year and lifetime prevalence of AUD using data from the 2012-2013 National Epidemiologic Survey on Alcohol and Related Conditions III (NESARC-III), which collected information from face-to-face interviews with over 36,000 adults 18 years of age or older. The authors investigated the prevalence of AUD in various demographic groups and describe the marked disabilities associated with AUD. Only a small minority of those suffering from AUD seek treatment even though treatments can be effective.

The investigators also examined the relationship of AUD to other substance use disorders.  Many psychiatric and medical issues associated with AUD are compounded when alcohol is combined with other substances. Unfortunately, such combinations are common, and the data from this study reinforce the fact that the use of alcohol is associated with increased use of other substances including marijuana.

In another recent article  published in JAMA Psychiatry, Deborah Hasin and colleagues report an increase in the past-year prevalence of the use of marijuana. Based on the data the group analyzed, it appears that the rates have more than doubled in all age groups over the last 10 years.

What are the rates of AUD and marijuana use disorders in young adults over a recent one-year period? The Grant group found that the past-year prevalence rate of AUD was about 27% in 18 to 29 year olds. Rates of moderate and severe AUD over the past year were 6.5% and 7.1%, respectively. The Hasin group found that over 20% of 18 to 29 year olds used marijuana; the past-year prevalence rate of marijuana use disorders was about 7.5% in this age group. Over 20% of those with an alcohol use disorder also use marijuana, and many of these individuals suffer from both alcohol and marijuana use disorders.

As more states legalize the medical and recreational use of marijuana and its use becomes more socially acceptable, it is reasonable to ask whether more people will be under the simultaneous influence of both alcohol and marijuana. Based on analyses in the Grant and Hasin papers, this seems probable. Where recreational marijuana is legal, it is also likely that there will be an increase in private clubs catering to marijuana users. Even if drinking is prohibited in such establishments, it remains likely that many patrons will use both recreational drugs. The effects of edible marijuana are delayed and relatively long lasting. There is nothing to prevent a person from ingesting marijuana and then consuming alcohol, or vice versa.

Now let’s turn our attention to driving. The adverse effects of alcohol on driving are well known. Even one or two drinks can interfere substantially with driving performance. This is true even though that amount of alcohol is unlikely to cause blood alcohol levels to reach the legal limit in terms of driving.

The influence of marijuana alone on driving performance is controversial. Lower doses may have variable effects on different individuals. Higher doses influence driving abilities more consistently. What about the effects of combining alcohol and marijuana on driving abilities? Marijuana and alcohol affect different cognitive and motor functions. The combination of the two drugs, even at relatively low doses, has the potential for additive or more than additive detrimental effects on driving skills.

As marijuana use becomes more commonplace, will there be more accidents related to driving under the influence of the combination of alcohol and marijuana? We are concerned that this is likely.

Only time will tell.

This column was written by Eugene Rubin MD, PhD and Charles Zorumski MD.

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