A study of nearly 800 individuals prescribed medical marijuana for chronic pain showed more than half reported driving within 2 hours of use. About the same proportion said they drove “a little high,” and about one in five reported driving “while very high.”

“I was particularly interested in understanding how people using [cannabis] medically may also be engaging in this risky behavior,” Erin E. Bonar, PhD, University of Michigan Addiction Center and assistant professor of psychiatry at the University of Michigan School of Medicine in Ann Arbor, told Medscape Medical News.

The findings were published online late last week in Drug and Alcohol Dependence.

A meta-analysis published in 2016 called attention to the public health risks associated with driving under the influence of cannabis (DUIC), including a potential increase in motor vehicle accidents.

However, another meta-analysis published last year revealed that cannabis use was not significantly related to “unfavorable traffic events,” including motor vehicle accidents.

“Although prior literature regarding DUIC is mixed, rapidly shifting cannabis policies in the US warrant greater attention to this important public health issue,” the current researchers write.

“There is an urgent need to better understand DUIC in order to inform future prevention efforts,” they add.

Bonar and colleagues recruited participants 21 years and older seeking certification or recertification for medical marijuana. The 790 patients (mean age, 46 years; 52% men; 81% white) came from three medical cannabis centers in Michigan between February 2014 and June 2015.

Most of the participants were unemployed (61%), and 32% were receiving disability benefits.

The current study is the first in which people using medical cannabis were asked about their driving, Bonnar said. It is also part of a larger, long-term study of patients taking medical marijuana.

“The aim is to follow them over time and see what happens to them after they get a card or renew their card, including health outcomes, mental health outcomes, and behaviors,” Bonar reported.

The investigators asked about cannabis use, for example, in terms of hours high per day and average quantity per week in the previous month.

They also asked participants the number of times in the past 6 months they drove “within 2 hours of using marijuana,” “while a little high on marijuana,” or “while very high on marijuana.” Possible responses ranged from “never” to “more than 10 times.”

Nearly three quarters of participants (73%) reported using cannabis daily or almost daily in the previous 6 months. At the same time, 56% drove within 2 hours of cannabis use, 51% drove while a little high, and 21% drove while very high.

White individuals had a greater likelihood of DUIC within 2 hours or while a little high compared with other participants, logistic regression analyses indicated.

Age also played a factor, with younger adults at greater risk for DUIC. In addition, higher pain scores were associated with lower odds of DUIC.

“The thing that most piqued my interest or concerned me was not just the amount of people who said ‘Yes, I drove while a little high’ or ‘I drove while really high,’ but [that] some people did that frequently,” Bonar said.

In the group who drove under the influence of medical cannabis more than 10 times in the previous 6 months, 22% reported driving within 2 hours of cannabis use, 19% drove while a little high, and 7% drove while very high.

Patients who take medical cannabis may be at particularly high risk for DUIC because of their high frequency of use, the researchers note.

In addition, 4% of all participants reported a lifetime history of arrest for DUIC.

The setting in which participants were asked about driving behaviors — the clinical visit for medical cannabis certification or recertification — could be an ideal opportunity to counsel patients about risks, the investigators note.

SOURCE: https://www.medscape.com/viewarticle/907521#vp_3

REFERENCE: Bonar et al: Driving under the influence of cannabis among medical cannabis patients with chronic pain; https://www.sciencedirect.com/science/article/pii/S0376871618308263?via%3Dihub