A new study on marijuana appeared in Journal of the American Heart Association. These are interesting data, but we have to interpret them very carefully.
Sure, we know cannabis can raise heart rate briefly, but most users develop tolerance to the effect. We’ve also seen (in a much larger sample) that it doesn’t increase mortality rates even among survivors of heart attacks.
But the new study made the news anyway. Investigators specifically searched a French database where physicians are legally bound to report any drug-related case that they view as “leading to temporary or permanent functional incapacity or disability, to inpatient hospitalization or prolongation of existing hospitalization, to congenital anomalies, or to an immediate vital risk or death.”
They then looked for cannabis users and found a shade less than 2,000 in the past 5 years. It’s impossible to know what that number means without knowing the number of people these physicians saw or how many patients used cannabis and did not end up reported to this database.
They then found a whopping 35 of these who had cardiac complications. It is impossible to know what to make of this number without knowing the number of cannabis users in France, which the authors report is 1.2 million. If you divide 35 by 1.2 million you get roughly .00003. I’m guessing that not all these cannabis users went to the doctor and not every person who used cannabis and had cardiac complications fessed up to the doctor, so let’s say that we’re off by two orders of magnitude. Let’s give the prohibitionists the benefit of the doubt and multiply by 100. That’d put the rate of problems up to .003.
If those are the chances of having cardiac complications as a French cannabis user, my first thought is that using cannabis protects people from cardiac problems. We need a comparison group of people who don’t use cannabis to know their rate of cardiac problems, but, as the authors point out, we simply don’t have those data. The closest estimates were 57 per 10,000 people, based on another study, which is .0057, or almost twice as bad as the rate among the cannabis users (after our generous overestimation). I’m not going to hold my breath for the the headline, “Cut your heart disease in half with cannabis.”
In short, this study tells us a lot about what kinds of cardiac complications appeared in people who were reported to the French government for cannabis-related problems, but tells us little about the link between cannabis use and cardiovascular disease.
The enactment of state laws legalizing the physician-recommended use of cannabis therapy is not associated with increased levels of marijuana use by young people, according to data published online in the Journal of Adolescent Health.
Researchers at Rhode Island Hospital and Brown University assessed the impact of medical cannabis laws by examining trends in reported drug use by high-schoolers in a cohort of states before and after legalization. Researchers compared these trends to geographically matched states that had not adopted medical marijuana laws.
Authors reported overall “no statistically significant differences in marijuana use before and after policy change for any state pairing,” and acknowledged that some states that had adopted medical cannabis laws experienced a decrease in adolescent’s self-reported use of the plant. “In the regression analysis, we did not find an overall increased probability of marijuana use related to the policy change,” they stated.
Investigators concluded, “This study did not find increases in adolescent marijuana use related to legalization of medical marijuana. … This suggests that concerns about ‘sending the wrong message’ may have been overblown. … Our study … may provide some reassurance to policy makers who wish to balance compassion for individuals who have been unable to find relief from conventional medical therapies with the safety and well-being of youth.”
A 2013 study published in the American Journal of Public Health similarly concluded that the passage of medical marijuana laws in various states has had no “statistically significant … effect on the prevalence of either lifetime or 30-day marijuana use” by adolescents residing in those states.
A 2012 study by researchers at McGill University in Montreal reported: “[P]assing MMLs (medical marijuana laws) decreased past-month use among adolescents … and had no discernible effect on the perceived riskiness of monthly use. … [These] estimates suggest that reported adolescent marijuana use may actually decrease following the passing of medical marijuana laws.”
Read the abstract of this latest study, “The Impact of State Medical Marijuana Legislation on Adolescent Marijuana Use,” online here.
Minnesota: African Americans Six Times More Likely Than Whites To Be Arrested For Marijuana PossessionApril 21, 2014
African Americans are arrested for marijuana possession offenses in Minnesota at a rate that is more than six-times higher than that of Caucasians, according to an analysis of 2011 FBI arrest data released today by the nonpartisan think-tank Minnesota 2020 and commissioned in part by Minnesota NORML.
Although African Americans comprise less than six percent of the state’s population, they represented over 27 percent of those persons arrested for violating marijuana possession laws in 2011. By comparison, whites comprise some 87 percent of the state’s population and constituted 69 percent of those arrested for violating marijuana possession laws. “Thus, the black arrest rate for marijuana possession was 687 and the white arrest rate was 107, making blacks 6.4 times more likely to be arrested for marijuana possession than whites,” the study found.
In 2010, blacks in Minnesota were arrested for cannabis possession at 7.8 times the rate of whites. Both African Americans and Caucasians consume cannabis at approximately similar rates.
The racial disparity in Minnesota in marijuana possession arrests is significantly higher than the national average. According to a 2013 analysis of marijuana possession arrests by race in 945 counties nationwide, blacks are approximately four times as likely as whites to be arrested for marijuana possession.
“[This] kind of over-representation cannot be accounted for without racial bias,” Minnesota 2020 Executive Director Steve Fletcher said today at a press conference. “It means black Minnesotans are bearing a disproportionate share of the personal and collateral costs of our war on drugs.”
A variety of factors contribute to the disparity in arrest rates, the study found. These include “over-policing in communities of color, cultural differences in where or how marijuana is used and purchased, and [the prevalence] of grants and seizure policies that incentivize volume over quality in drug arrests,” the think-tank acknowledged in a press release.
The report estimated that the collateral costs of a low-level marijuana arrest may total as much as $76,000 over the course of a decade, including attorney fees, fines, costs associated with attending mandatory drug treatment, lost income and job prospects, and barriers to public assistance and federal aid.
“In light of these human and financial costs, Minnesota lawmakers and law enforcement officials have a responsibility to consider whether marijuana possession laws in their current conception are actually contributing to public safety, or if they are instead producing undue hardship for individuals and growing inequities within society,” the study concludes.
Full text of the study, entitled “Collateral Costs: Racial Disparities and Injustice in Minnesota’s Marijuana Laws,” is available online here.
The mainstream media launched into a reefer mad frenzy this week after researchers from Harvard University in Boston and Northwestern University in Chicago published the results of a neuroimaging study assessing the brains of a small cohort of regular marijuana smokers and non-users. The brain scans identified various differences between the two groups in three aspects of brain morphometry: gray matter density, volume, and shape. These differences triggered dozens of high-profile media outlets to lose their collective minds. Here’s a sampling:
Yet despite the sensationalist headlines, the study itself was hardly newsworthy. Decades of research pertaining to the potential residual adverse effects of cannabis on brain cognition have failed to support the notion that marijuana poses any sort of permanent brain deficits. And as I write today on Alternet.org, this study similarly failed to report any sort of real-world adverse consequences associated with cannabis use:
[excerpt] Using high–resolution MRI imaging, scientists identified specific changes in particular regions of the brain that they inferred were likely due to marijuana exposure. (Since researchers only performed a single MRI session, they could not say definitively whether these changes were, in fact, caused by cannabis or whether they existed prior to subjects’ use of the plant.) Notably, however, these changes did not appear to be associated with any overt adverse effects in subjects’ actual cognition or behavior. (Separate studies assessing youth use of legal intoxicants, such as nicotine and alcohol, have also been associated with documented changes in brain structure. Ditto for caffeine intake in preclinical models. These findings have received far less media attention.)
Both the cases (20 marijuana users) and controls (20 nonusers) in the study were recruited from local universities, undermining the notion that the alleged ‘brain damaged potheads’ were any more academically challenged than their non-using peers. Further, as summarized by HealthDay: “Psychiatric interviews revealed that the pot smokers did not meet criteria for drug dependence. For example, marijuana use did not interfere with their studies, work or other activities, and they had not needed to increase the amount they used to get the same high.”
In other words, case subjects and controls appeared to function similarly in their professional and academic endeavors.
You can read the full text of my response here.
[Update: I have a separate op/ed ("Smoke weed, turn into a pothead? Not so fast") responding to this paper online in The Los Angeles Times here.]
Fortunately, my critique of this latest paper — and in particular the mainstream media’s sensationalist and erroneous coverage of its findings — is far from the only one. Below are links to several other excellent analyses:
Bits of DNA (blog): Does researching casual marijuana use cause brain abnormalities?
By Mitch Earleywine, Ph.D
State University of New York at Albany
Chair, NORML board of directors
A new study claims to show small deficits on neuropsychological tests in college students who started smoking marijuana early in life. It might get a lot of press. Prohibitionists love to bang the drum of marijuana-related cognitive deficits, so I’d like NORMLites to know how to make sense of this sort of research. The recurring themes in this literature involve several alternative explanations that never seem to dawn on journalists. These results often arise from artifacts of the study rather than physiological effects of the plant. I’d like to focus on a few: other drug use, dozens of statistical tests, the incentives for performance, and the demands communicated by the experimenters.
The latest paper of this type is actually pretty good. Researchers studied over 30 people aged 18-20 who started using before age 17 (their average starting age was around 15) and who smoked at least 5 days per week for at least a year. They compared them to a comparable bunch of non-users. I hate to see 15-year-olds using anything psychoactive, even caffeine. Spending full days in high school with less than optimal memory functioning is no way to lay the groundwork for a superb life. I admit that I want these same people to grow up and be the next generation of activists, so feel free to call me selfish when I emphasize NORML’s consistent message: THE PLANT IS NOT FOR KIDS WHO LACK MEDICAL NECESSITY.
OTHER DRUG USE?
First, we have to keep other drug use in mind. Unfortunately, the marijuana group in this study got drunk more than 4 times as much in the last six months as the controls. Given what we know about binge drinking and neuropsychological functioning, it’s going to be hard to attribute any differences between these groups to the plant. It’s just as likely that any deficits stem from pounding beers. Studying cannabis users who aren’t so involved with alcohol would help address neuropsychological functioning much better.
HOW MANY TESTS?
In addition, we should always consider the number of measures in any study. Many of these neuropsychological tasks have multiple trials that can be scored multiple ways. The more statistical tests you run, the more likely it is that you’ll find a statistically significant difference by chance. It’s kind of like flipping coins. It’s rare to flip four heads in a row. But if you flip a coin a thousand times, odds are high that somewhere in the list of a thousand results will be four heads in a row. These investigators got 48 different test scores out of the participants. You’d expect at least 2 of them to be significant just by chance. They found differences on 14 different scores, suggesting that something’s going on, but we’re not sure which results are the “real” differences and which ones arose by accident. (That’s why we replicate studies like this.) And, as I mentioned, it might all be because of the booze.
WHY WOULD ANYONE DO ALL THESE TESTS?
We also have to consider incentives for performance. Most researchers bring participants to the lab for a fixed fee and ask them to crank out a bunch of crazy puzzles and memory assessments. It’s unclear why people would feel compelled to strain their brains. The authors of this study were kind enough to mention some relevant work by my friend (and former student) Dr. Rayna Macher. Dr. Macher showed that cannabis users respond best when you make the effort worth their while. She focused on people who used the plant at least four times per week for a year or more. She read one group some standard instructions for a memory test. The other group got the regular instructions plus an additional sentence: “It is important that you try your very best on these tasks, because this research will be used to support legislation on marijuana policy.”
As you’d guess, this simple sentence fired them up. Compared to cannabis users who didn’t hear that sentence, they performed better on 3 out of 10 measures. (You’d expect less than one difference by chance.) And compared to the non-users, the folks who got the incentive sentence did just as well on all the tests. For those who didn’t hear the incentive sentence, users did less well than non-users on 1 of the 10.
I know that prohibitionists are going to try to call this amotivation. (See my rant on that when you get a chance) I call it putting effort where it pays. But given what we know about how these studies can hamper the reform of marijuana laws, users everywhere should do their best on all tests whenever they get the chance.
WE OFTEN DO WHAT EXPERIMENTERS EXPECT OF US
Last but not least, we have to consider the demands communicated by the experimenter. Decades of data now support the idea that people often do what others expect them to do, especially if they believe the expectation, too. Another friend and former student, Dr. Alison Looby De Young, showed that these expectations are critical in studies of neuropsychological performance and cannabis. She gave a neuropsychological battery to men who had used cannabis at least three times per week for the last two years. One group of men read instructions that said that cannabis had no impact on their performance on these tests. Another group read instructions that said that cannabis was going to make them perform poorly. You guessed it, those men who heard they were going to flub the tests performed worse on 2 of the 4 tests. (You’d expect less than one difference by chance). As you might imagine, some laboratories communicate their expectations about cannabis and cognitive function subtly or not so subtly. Some participants are bound to behave accordingly. So what looks like a cognitive deficit is just an artifact of the laboratory environment where experimenters stare daggers at cannabis users.
In the end, I’m glad that researchers do this work, but these effects are too small and fleeting to justify prohibition. We already know that cannabis isn’t for healthy kids. People who get heavily involved with the plant early in life might not perform as well as those who never touch cannabis even if investigators control for other drug use, AND use a sensible number of tests, AND provide appropriate incentives, AND communicate a reasonable expectation.
But how many people should go to jail for that?
If you said, “None,” you’ve done an excellent job on an important cognitive test.