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New research on cannabis shows longer impairment effects beyond initial high

Potency and frequency of use of marijuana can have long-lasting negative effects on developing brains, pediatric psychiatrists say.
Feodora Chiosea

Dr. Ari Kirshenbaum wants cannabis users in Vermont to know he is not against making the drug legal for recreational use.

But the professor of psychology at St. Michael’s College in Colchester does want to remind people that cannabis is a drug, and that a new report from the American Psychological Association that he contributed findings to shows that impairment effects from cannabis use can last longer than many users may realize.

Vermont Public’s Mitch Wertlieb spoke with Dr. Kirshenbaum about the big takeaways from this new research.  Their conversation below has been edited and condensed for clarity.

Dr. Ari Kirshenbaum: We find with our research that even heavy users of cannabis, people who are using it daily, are still demonstrating signs of impairment after five hours post-use. So that means they can smoke a little bit and five hours later, we're still detecting some problems in their abilities to make good decisions, to operate motor vehicles, that kind of thing. I think that, at least with the data we have, we can infer that these impairments are going to be problematic that long after use. So just because you don't feel it doesn't mean that you're not impaired.

Mitch Wertlieb: When you see impairment in regards to cannabis ingestion, how might that differ, say, from alcohol intoxication? 

That is an excellent question. And I think that anybody who is a consumer of cannabis and alcohol knows that these drugs affect you differently. And certainly when it comes to the impairing effects of alcohol, we're, as a society, much more informed about what those are. When it comes to cannabis, I think that we're not well informed. Kind of like if you think about driving down an icy road, you're driving down the icy road, your vehicle might slip and you make that immediate compensation. And that particular activity, that particular kind of reaction is impaired by cannabis as well. And other things include issues having to do with impulse control. That might be one. And certainly attention and concentration difficulties are there too.

I'm curious about what quantities and what forms of cannabis you tested, when it came to impairment. 

I've tested cannabis impairment in a number of different areas. One, we did a sort of a clinical study in which we had people arrive to a testing site, and they used their own cannabis and smoked the way that they typically would. And then we had that run through our software to detect these signs of impairment. And in that particular study, it varied but we wanted people to bring their own cannabis, what they were most accustomed to, to see if we could still detect impairments there, and we could.

I'm curious, too, about what motivated this research? Is it based on data from any increase in things like road accidents or criminal behavior that might be linked to cannabis use? Or did you decide to study the impairment effects as more of a caution for these potential problems? 

I think that as a society, we're ill-prepared to deal with the change in public policy. I'm not saying I disagree. In fact, I agree with the shift of public policy because our former public policy, where it was criminalized in the state of Vermont, was not predicated on protecting civil liberties. This was not predicated on science. So I think where we are is where we should be.

But I also think that we just are not very well informed about cannabis in general as a society. So for instance, one thing I'd like to point out is that cannabis is dependence-producing. People will suffer withdrawal if they’re chronic, habitual daily users of cannabis, and they decide to discontinue their use. There is a withdrawal syndrome. And I think that sometimes challenges people's notion that cannabis is a harmless drug. It's not. When it comes to driving or operating heavy equipment, I also want people to be aware — just to have an acute awareness that they're not operating with their full functionality.

I mean, we're still in the early days of this here in Vermont. The cannabis marketplace only opened up last October. What do you think this research means for the state's approach to cannabis use and to its accessibility?

That is a great question. And really, when it comes to the state, I don't know. I'm not working with anybody directly with the state at this point to know how well-prepared we are to deal with the ramifications of legalized weed.

Well, who do you hope sees these findings? I mean, if not state officials, you know, certainly Gov. Phil Scott, kind of reluctantly, allowed retail cannabis to become the law here. He had some concerns about some of the very things you're talking about like road impairment, driving a car, etc. So, who is this designed for, this study? 

We are past that legalization, at least in Vermont. We are in a 421 world. And now I think that individual users have the burden associated with their use where they have to be responsible adults who are fully informed and ready to accept the consequences of our actions. And that comes to sort of becoming more aware that cannabis is dependence-producing. Cannabis impairs our ability to function, and a host of other things.

Dr. Kirshenbaum, isn't there another side to this coin, though? And that's because there are reported benefits of cannabis use from things like pain management, anxiety reduction, other medicinal uses. Are you concerned that these kinds of studies might be discounting those other medical benefits which many people have found to be very beneficial? 

Oh, absolutely. Federally, cannabis is still a Schedule I drug which means that it doesn't have any medicinal use, and we know that it has medicinal use. But I think we need to be careful with what we consider to be medicinal use. Anytime we use cannabis, it is palliative, meaning that it's treating symptoms. It’s not going to treat the cause. For instance, you can't smoke a bong and expect to cure your lung cancer. It's just not the way it works. But certainly symptom reduction is very important. But there are a whole host of medications out there that we use for pain management that also impair our driving. We need to be worried about those, too. So I don't want to demonize cannabis at all. But I do want to have a more nuanced, more informed approach to how we use cannabis as individual consumers.

Have questions, comments or tips? Send us a message.

A graduate of NYU with a Master's Degree in journalism, Mitch has more than 20 years experience in radio news. He got his start as news director at NYU's college station, and moved on to a news director (and part-time DJ position) for commercial radio station WMVY on Martha's Vineyard. But public radio was where Mitch wanted to be and he eventually moved on to Boston where he worked for six years in a number of different capacities at member station a Senior Producer, Editor, and fill-in co-host of the nationally distributed Here and Now. Mitch has been a guest host of the national NPR sports program "Only A Game". He's also worked as an editor and producer for international news coverage with Monitor Radio in Boston.
Karen is Vermont Public's Director of Radio Programming, serving Vermonters by overseeing the sound of Vermont Public's radio broadcast service. Karen has a long history with public radio, beginning in the early 2000's with the launch of the weekly classical music program, Sunday Bach. Karen's undergraduate degree is in Broadcast Journalism, and she has worked for public radio in Vermont and St. Louis, MO, in areas of production, programming, traffic, operations and news. She has produced many projects for broadcast over the years, including the Vermont Public Choral Hour, with host Linda Radtke, and interviews with local newsmakers with Morning Edition host Mitch Wertlieb. In 2021 Karen worked with co-producer Betty Smith on a national collaboration with StoryCorps One Small Step, connecting Vermonters one conversation at a time.
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