It was less than a year ago when the mainstream media was chock-full of headlines like this one: ‘Brain changes associated with casual marijuana use in young adults, study finds.’ The alarmist headlines were in response to a controversial paper published by researchers at Harvard University in Boston and Northwestern University in Chicago which alleged to have found differences in brain morphology in a cohort of 20 college-age marijuana users as compared to 20 non-users. The study’s investigators attributed the differences to subjects’ cannabis use.
But a funny thing happened when a team of scientists from the University of Colorado and the University of Kentucky tried to replicate these results in a separate, larger sample (158 participants) of subjects after rigorously controlling for both groups’ use of alcohol.
Writing in the January 28 edition of The Journal of Neuroscience, authors summarized:
“[T]his retrospective study examined brain morphology in a sample of adult daily marijuana users (n = 29) versus nonusers (n = 29) and a sample of adolescent daily users (n = 50) versus nonusers (n = 50). Groups were matched on a critical confounding variable, alcohol use, to a far greater degree than in previously published studies.
We acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum.
No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect.”
Why the contradictory results? Investigators speculated that previously reported imaging studies failed to adequately control for the impact of alcohol, a substance that “unlike marijuana, … has been unequivocally associated with deleterious effects on brain morphology and cognition in both adults and adolescents.” In other words, researchers theorized that previously reported differences in the brain images of marijuana consumers as compared to non-users were likely because of subjects consumption of booze, not cannabis.
They concluded, “In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures. … [I]t seems unlikely that marijuana use has the same level of long-term deleterious effects on brain morphology as other drugs like alcohol. The press may not cite studies that do not find sensational effects, but these studies are still extremely important.”
An abstract of the study, “Daily Marijuana Use Is Not Associated with Brain Morphometric Measures in Adolescents or Adults,” is online here.
Among those voters age 18 to 40, 47 percent ranked alcohol as the most harmful substance to society, well ahead of both tobacco (27 percent) and cannabis (13 percent). (Thirteen percent of respondents were undecided.) Respondents among all age and ethnic groups were consistent in ranking marijuana as the least harmful of the three substances, as were self-identified Democrats and Independents. (Republicans rated tobacco to be the most harmful of the three products.)
“[These] numbers suggest younger Americans are upending societal conventions, which have long seen alcohol as an acceptable drug while condemning marijuana,” stated Rare.us in an accompanying press release.
The results are somewhat similar to those of a Wall Street Journal/NBC News poll released in March which reported that most Americans believe tobacco to be most harmful to health (49 percent), followed by alcohol (24 percent), sugar (15 percent), and marijuana (8 percent).
Under federal law, marijuana is classified as a schedule I controlled substance, meaning that its alleged harms are equal to those of heroin. Both tobacco and alcohol are unscheduled under federal law.
According to a study published in 2004 in the Journal of the American Medical Association, the leading causes of death in the United States ware tobacco (435,000 deaths; 18.1 percent of total US deaths), poor diet and physical inactivity (365,000 deaths; 15.2 percent), and alcohol consumption (85,000 deaths; 3.5 percent).
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.
Those who report consuming cannabis two or three times per week are less likely to engage in at risk drinking behavior, according to data published online in The American Journal of Addictions.
Investigators from Sweden’s Lund University, Department of Clinical Sciences, analyzed data from a nationwide survey on alcohol and drug use conducted by the National Institute of Public Health. Over 22,000 respondents between the ages of 15 and 64 participated in the survey.
Researchers reported that frequent cannabis consumers (defined as having used cannabis two or three times per week) were less likely to engage in hazardous drinking practices compared to infrequent users (those who reported having consumed cannabis fewer than four times per month).
They concluded: “In the present study, it has been shown that, in the Swedish general population, cannabis use is associated with a higher prevalence of other illicit drug use and hazardous alcohol use. Among cannabis users, frequent cannabis use is associated with a higher prevalence of other illicit drug use and a lower prevalence of hazardous alcohol use when compared to occasional cannabis use. … … The inverse relationship between the frequency of cannabis use and hazardous drinking has not been reported before to our knowledge. … This may indicate that cannabis users and alcohol users are different groups, albeit with a high degree of overlap between groups, with different characteristics and clinical needs.”
A review paper published in February in the journal Alcohol and Alcoholism similarly acknowledged that some cannabis consumers likely substitute the plant for alcohol. It concluded: “While more research and improved study designs are needed to better identify the extent and impact of cannabis substitution on those affected by AUD (alcohol use disorders), cannabis does appear to be a potential substitute for alcohol. Perhaps more importantly, cannabis is both safer and potentially less addictive than benzodiazepines and other pharmaceuticals that have been evaluated as substitutes for alcohol.”
An abstract of the study, “Alcohol and drug use in groups of cannabis users: Results from a survey on drug use in the Swedish general population,” appears here.
Seventy-five percent of Americans believe that the sale and use of cannabis will eventually be legal for adults, according to national polling data released this week by the Pew Research Center. Pew pollsters have been surveying public opinion on the marijuana legalization issue since 1973, when only 12 percent of Americans supported regulating the substance.
Fifty-four percent of respondents say that marijuana ought to be legal now, according to the poll. The total is the highest percentage of support ever reported by Pew and marks an increase of 2 percent since 2013. Forty-two percent of respondents said that they opposed legalizing marijuana for non-therapeutic purposes. Only 16 percent of Americans said that the plant should not be legalized for any reason.
Demographically, support for cannabis legalization was highest among those age 18 to 29 (70 percent), African Americans (60 percent), and Democrats (63 percent). Support was weakest among those age 65 and older (32 percent) and Republicans (39 percent).
Seventy-six percent of those surveyed oppose incarceration as a punishment for those found to have possessed personal use quantities of marijuana. Only 22 percent of respondents supported sentencing marijuana possession offenders to jail.
Fifty-four percent of those polled expressed concern that legalizing marijuana might lead to greater levels of underage pot use. (Forty-four percent said that it would not.) Overall, however, respondents did not appear to believe that such an outcome would pose the type of significant detrimental health risks presently associated with alcohol. As in other recent polls, respondents overwhelmingly say that using cannabis is far less harmful to health than is drinking alcohol. Sixty-nine percent of those polled said that alcohol “is more harmful to a person’s health” than is marijuana. Only 15 percent said that cannabis posed greater health risks. Sixty-three percent of respondents separately said that alcohol is “more harmful to society” than cannabis. Only 23 percent said that marijuana was more harmful.
The Pew poll possesses a margin on error of +/- 2.6 percent.
Commenting on the poll, NORML Deputy Director Paul Armentano said: “Advocating for the regulation of cannabis for adults is not a fringe political opinion. It is the majority opinion among the public. Elected officials who continue to push for the status quo — the notion that cannabis ought to be criminalized and that the consumers of cannabis ought to be stigmatized and punished — are holding on to a fringe position that is increasingly out-of-step with the their constituents’ beliefs.”