Drunk and Stoned Behind the Wheel: Double the Driving Risk

Posted on July 18th, 2016
Posted in Substance Abuse

Awareness of the dangers of drinking and driving tends to increase during certain times of the year, especially around holidays, proms, and summer vacations. With four states and the District of Columbia now legalizing recreational marijuana use and other states considering putting measures on the ballot to legalize pot for recreational use, there’s more awareness about marijuana in total. Not much in the way of research has been conducted on the dangers of drinking and smoking pot and then getting behind the wheel — until now.

Addiction.com’s Suzanne Kane spoke with Meenakshi Subbaraman, PhD, associate scientist and biostatistician at the Alcohol Research Group in Emeryville, California about her study on the co-use of alcohol and cannabis and its effect on driving.

Suzanne Kane (SK): Why did you do this study?

Meenakshi Subbaraman (MS): I did this study because no one yet had directly compared people who tended to use alcohol and cannabis together versus those who tended to use them separately — and also compared to people who just drink alcohol and don’t use pot. I was interested in comparing those three groups in the general population in terms of their risks of drunk driving and other harms.

SK: What are the most important findings relative to simultaneously drinking alcohol and smoking pot then driving?

MS: The most important finding is that people who tended to drink alcohol when they smoked pot had double the odds of drunk driving and other harms, compared to both those who only drank alcohol and compared to those who would use alcohol and pot, but always separately. Taking out the driving part, these were people who reported that they had drank in the past 12 months and that they had used pot in the last 12 months, but they had always used them separately.

Then we had this group of interests, which were the people who also reported drinking and using pot in the past 12 months, but they tended to drink when they used marijuana. They were using them together. That doesn’t mean they always used pot when they drank. The question was worded such that it was more asking about drinking while using pot, and not vice versa. Did you drink while you used pot? Not, did you use pot while you drank?

There were other social consequences and harms that also appeared to be more prevalent in the group that used the two together. These were things like getting into arguments, getting in trouble at work, [and getting arrested for driving after drinking, drinking contributed to getting hurt in an accident in a car or elsewhere, etc.]. We didn’t look at these harms individually. We looked at them on a scale.

If cannabis use becomes more prevalent as U.S. states and other countries continue to legalize it, then we need to be prepared to advise people appropriately. If you use both substances together, your risk of drunk driving, and possibly other consequences, may be higher than if you stick to using one at a time.

SK: What are the signs of co-use? Are they easily recognizable?

MS:  Other research not based on my paper has found that physical signs are not so different than if you were just drinking or just smoking. There’ve been studies looking at objective measures like heart rate or dilated pupils and also more subjective measures like self-reported intoxication. Combining the two, they haven’t necessarily found significant differences among those who use them together or use them separately. [As for detection], there are alcohol tests [and] they’re coming out with tests for THC and cannabinoids in blood that could be used on the roadside.

SK: Do you see this trend increasing at a rapid pace due to legalization of recreational marijuana in some states, for example, or in states where medical marijuana is legal?

MS: Not necessarily. I also don’t think that you could necessarily call it a trend. We didn’t look at how this is changing over time. I think there are more and more studies coming out showing that people would actually be substituting pot for alcohol and just not drink in places where they’re legalizing or decriminalizing marijuana. I think it’s highly possible that people might actually drink less, so we might not see, necessarily, that co-use would increase, but we might see that alcohol use decreases.

SK: What should treatment facilities know about treating alcohol addiction and cannabis addiction? For example, should they screen for and treat both simultaneously?

MS: Maybe. The research on people in alcohol treatment, and I’ve done a lot in this area, the findings are really mixed in terms of how pot use affects individuals in treatment for alcohol use disorders. There are some studies that find that pot use makes alcohol outcomes worse. There are an equal number of studies that are just as solid and scientifically rigorous that show that people in alcohol treatment can actually benefit from pot use in terms of their alcohol use. They would substitute and reduce their alcohol use. I would say that maybe the most important message for treatment facilities is not to kick people out of treatment if they screen positive for cannabis but rather try and understand those motives. When you kick people out for testing positive for pot when they’re in treatment for alcohol, it really deters them from trying to get help and it prolongs their alcohol use disorders. That policy should be re-examined.

Most importantly, though, the findings [from this study] will help clinicians and prevention/treatment specialists advise patients and others in the community regarding the elevated risk of consequences related to simultaneous use. I also hope that as the cannabis industry continues to grow, manufacturers will consider some sort of warning label related to increased risks when mixing alcohol and cannabis.

SK: What’s next in terms of studies in this area of the risks and dangers of co-use of alcohol and cannabis?

MS: What’s next is looking at these really specific consequences, like getting into legal trouble, having your doctor ask you to cut down on alcohol. I think looking at those specific harms and consequences is important. Also, looking at states where legalization is happening and trying to get a good understanding whether there is a trend of increased marijuana use because of legalization and, more importantly, maybe of increased co-use of marijuana and alcohol in states where it’s legal.

We’re gathering data here [at the Alcohol Research Group] in states like Washington, looking at individual level of alcohol use and cannabis use and combined use, both before and after the policy changes. In the next year or two, we’ll have a better idea whether there is a trend and how people’s substance use behaviors may or may not be changing relative to these policy changes.

A Final Point Worth Making

When asked to comment about the dangers of drinking and smoking pot and getting behind the wheel, Amy George, senior vice president of marketing and communications for Mothers Against Drunk Driving, tells Addiction.com: “Alcohol is a drug and continues to be the leading substance for impairment and crash risk on the roads. At the same time, we want everyone to know that drunk or drugged driving deaths and injuries are 100 percent preventable every time.”

By Suzanne Kane

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