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Cannabis Campaigners' Guide News Database result:
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No, A Study Didn't Say Cannabis Impairs Driving Once You're Sober
Forbes Friday 17 Jan 2020 This week, for example, dozens of media outlets referenced a recent small study on cannabis and driving under various headlines, suggesting the study found that long-term, early, or even any cannabis use may cause impaired driving in the days or years to come. It found none of these things. If you only read certain news articles about it, or (to be fair) the potentially misleading title and top points of the study — or if you’re not used to decoding scientific studies generally — that fact is easy to miss. For cannabis medical patients who, for example, carefully monitor their use and were reasonably planning to drive the kids to soccer practice tomorrow, the popular but erroneous interpretation of this study’s results may also be deeply disturbing. The study in question, prepared by researchers at Harvard’s Marijuana Investigations for Neuroscientific Discovery (MIND) Program, aimed to explore (in a preliminary way) whether heavy cannabis users who began using the plant earlier in life display poorer driving habits than heavy users who started later, or those who don’t use at all. To test this hypothesis, they recruited 28 people who they defined as heavy cannabis users, and 16 ‘healthy control’ (HC) participants, meaning they don’t use cannabis nor have any known health problems. Cannabis users couldn’t have used the drug for at least 12 hours, and researchers administered triage-quality rapid drug tests (such as police or EMTs might carry) to ensure their cannabis-using subjects really use it, and HCs really don’t. Cannabis users’ reported intake ranged from ~1 to 11 grams a week. These 44 people who live near Boston, ranging from about 18 to 30 years old, were then asked to complete a driving simulation — complete with fake chair, fake wheel and pedals, and a 19-inch monitor showing a simulated roadway — so that their performance could be measured in terms of lane use, speeding, hitting pedestrians, observing road signals, and a few other metrics. Results showed that heavy cannabis users in that group were slightly more likely to miss stop signs, speed, and hit the animated pedestrians; other driving metrics were about the same between groups. Cannabis users also completed the simulation more quickly. Apparently none of the participants made any illegal turns. As part of their fairly extensive analysis of the fairly limited data they gathered, researchers also divided heavy cannabis users into two groups: those who started using it at the age of 16 or younger, and those who started after that. Broadly speaking, the early-use group performed the worst in those areas where driving habits diverged. Researchers had also asked participants to complete a separate behavioral survey tied to impulsiveness, which they then compared to subjects’ cannabis histories. As it happens, cannabis users self-reported that they had somewhat lower attention spans and higher non-planning tendencies (i.e. impulsiveness) than non-users. At best, this study could be seen as a pilot for further investigation down the road, according to cannabis and research experts who’ve weighed in this week — in part, perhaps, because of certain questionable methods or decisions therein, which researchers would do well to avoid in the future if accuracy is what they’re after. For one thing, it’s important to recognize what the study did and didn’t seek to examine, and exactly what that study found, or did not. Paul Armentano, Deputy Director for the cannabis reform nonprofit NORML, commented by email, “To be clear, this paper identifies differences in driving behaviors between non-users and those who acknowledge being heavy users of cannabis and having begun their use prior to the age of 16. But, as acknowledged by one of the paper’s authors, differences in driving style should not be conflated with driving impairment.” Armentano pointed to The Boston Globe’s coverage as more accurate and nuanced than most: “[The] researchers, led by Drs. Mary Kathryn Dahlgren and Staci Gruber, cautioned their paper does not prove heavy, early users are functionally impaired behind the wheel on real-world roads,” reporter Dan Adams wrote. “What we’re seeing is relatively poor performance in early users compared to our non-using controls, but not necessarily impairment,” Dahlgren told the paper. What many news outlets also haven’t considered, Armentano said, was the idea that the self-identified or demonstrated ‘impulsiveness’ of early cannabis users “would seem to be more likely to be associated with an underlying personality trait than a direct cause-and-effect result of early onset cannabis exposure.” In other words, he said, “Those individuals who are generally more impulsive and less risk averse would be more likely to engage in cannabis use at a young age, and they would also be more likely drive in a risky manner” — and the latter is something that younger folks are statistically more prone to do versus older folks, anyway. When it comes to crunching the data, there also seem to be several factors that either researchers or the media may not have considered. Sheila Vakharia, Deputy Director of the Department of Research and Academic Engagement for the nonprofit reform group Drug Policy Alliance, pointed out in a phone interview that once participants’ level of impulsivity was factored in, there were no longer any statistical differences between the way cannabis users drove and non-cannabis users did. In addition, it seems somewhat counter-intuitive (or at least odd) that the researchers made sure their subject groups were pretty well matched in terms of age, IQ, and alcohol usage, but not their gender: the HC group consisted of six men and 10 women, while the cannabis-using group had 23 men and just five women. Such an imbalance could easily impact the results of a cannabis-and-driving study, as well as the conclusions it leads us to make. For example, “Studies have shown that women get into fewer accidents, and file fewer insurance claims,” Vakharia said — for whatever reasons this may be, and cited here without wanting to fuel gender stereotypes, but simply because it may be important to our understanding. Women are also conditioned in this society — from a young age, and throughout their lives — to behave more carefully and conservatively. Armentano also commented, “It is well established that males, particularly young men, possess elevated risk of accident. That is why the National Highway Traffic Safety Administration, in their gold-standard study of the issue of drugged-influenced driving and accident risk, adjusted for gender, after which the elevated risk associated with cannabis and motor-vehicle crash became all but insignificant.” It’s probably worth noting, too, that the level of cannabis usage among participants, both reported and observed in their urine tests, varied widely. Cannabis users’ Urinary THC/Creatinine Ratio was found to be 480.58 nanograms per milliliter on average, give or take another 663.56 ng/ml. In terms of helping inform US road safety measures, Vakharia said, “I don’t know how helpful this, except for flaring up potential stigma and concerns about enforcement.” With regard to researchers’ calculated margin of error for each data point, it also seems they may have chosen not to apply what’s known as the Bonferroni correction: a method for refining the acceptable margin of error when running multiple analyses on the same data (which they did), which can lead to false conclusions over time. If she were designing a study to investigate the long-term impacts of heavy cannabis use on driving, Vakharia said, it would be a longitudinal study — examining subjects over a long period of time — rather than cross-sectional, and would consider whether heavy cannabis users have underlying conditions (or, in relation to when they started cannabis, preexisting ones) related to their use. It would also subject participants to “a battery of tests” to establish their base-level coordination, muscle tone, prescription medication use, and other factors that could impact driving scores. One thing that’s clear today, however, is that causing alarm among regulators and the public before we have all the facts can cause serious problems for all down the road. And especially with booming areas of study, like cannabis science, it’s important to remember that not all data will have the same quality, nor will they always agree. To wit, “Other driving simulator studies fail to show any change in driving performance in subjects following several hours of abstinence,” Armentano wrote. “That said, no one advocating for adult-use cannabis regulations is opining that young people use or have easy access to cannabis; just the opposite. Regulating adult-use access is a way to impose necessary controls to the cannabis market so that society can better limit and discourage young people from misusing cannabis.” “It has long been a principle of NORML to discourage anyone from operating a motor vehicle under the influence of any substance,” he continued. “NORML has long advocated for providing law enforcement with better education and better tools — such as the use of hand-held performance technology like DRUID — to better identify such drivers and remove them from the roadways.” Overall, Vakharia said, it’s important to take “more than a grain of salt” with early studies, and particularly those with a small sample size, limited information on the participants, or representing just a cross-section or “snapshot” of their topic. One potential and worrying outcome of the kind of news coverage we’ve seen this week, Vakharia said, may be “causing people to feel that if they regularly use [cannabis] then they are fundamentally different than others even when they’re not under the influence” — something that research, and thousands of years of human experience, has given us no reason to believe. “It’s a slippery slope,” she added. “No one wants people under the influence putting others and themselves at risk, and a study like this can scare a lot of people who are well-intentioned, care a lot about public safety, and care a lot about published studies, so they assume this must have larger implications.” “A small study like this can maybe suggest potential correlation, but not causality,” Vakharia continued. “We need more studies, we need bigger studies, and we need better studies.” In terms of potentially misleading the public, it also seems worth noting that researchers chose — based on previous successes with doing so — to tell cannabis-using participants that their urine test could reveal if they had used cannabis in the last 12 hours, as a way of ensuring that such participants had abstained, and weren’t intoxicated. Of course, even more sophisticated tests can’t pinpoint cannabis use so precisely, let alone triage-quality tests. For the sake of their own and their friends or families’ informed-ness going forward, one only hopes that participants knew better. https://www.forbes.com/sites/janetwburns/2020/01/17/no-studies-didnt-find-cannabis-impairs-driving-once-youre-sober/#2e843d7d1134
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