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2016 wasn’t exactly a great year for many people, but for the booming legal cannabis industry, there were some historic victories. Not only did eight of nine states approve ballot measures for adult-use or medical cannabis in November, but there’s been quite a bit of interesting research related to the effects of cannabis legalization.

Contrary to the dire predictions of prohibitionists, society is not crumbling due to the fact that hundreds of millions of Americans live in states with legal medical or adult cannabis. In fact, many studies are showing that ending prohibition may have a number of positive outcome for societal health (beyond increased freedom and tax revenue).

Below is a short summary of four studies from this past year that show 2016 wasn’t all bad.

Cannabis Study #1: The Effect of Medical Marijuana on Sickness Absence

The Effect of Medical Marijuana on Sickness Absence
Major finding:
Workplace absences due to sickness decline following legalization of medical cannabis.

This study utilized the Current Population Survey, a monthly survey of ~60,000 U.S. households conducted by the Census Bureau, to look at the association between medical cannabis legalization and workplace absences. It was partially motivated by a previous study which found that alcohol consumption declined following medical marijuana legalization.

Since heavy drinkers have more work absences, and many people claim that medical cannabis provides them with relief from symptoms that cause workplace absences, one hypothesis was that states that legalized medical cannabis would see a decrease in workplace absences. Alternatively, easier access to cannabis might just turn people into stoned slackers, and therefore increase workplace absences.


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After enactment of medical cannabis laws, there was a modest but statistically significant decline in workplace absences due to sickness (after controlling for race, marital status, age, and education level). Moreover, the decline was largest for demographics that are most likely to hold medical cards (middle-aged males).

States with legal medical cannabis were also divided into those with “lax” laws, which provide easier access to medical cannabis (e.g. California, Colorado, Michigan, etc.), and “strict” states with fewer medical card holders and tougher regulations (e.g. New Jersey, Maine, D.C., etc.). States with lax laws saw a larger decrease in sickness-related absences from work.

While this type of study can’t establish a causal relationship between medical cannabis and workplace absenteeism, it adds to a growing number of studies that point to favorable associations between the implementation of medical cannabis laws and positive societal outcomes. These include a decrease in alcohol consumption and traffic fatalities, as well as suicides (especially among young adult males). Such results often directly contradict predictions that have routinely been made by prohibitionists.

Cannabis Study #2: Medical Marijuana Laws Reduce Prescription Medication Use in Medicare Part D

Medical Marijuana Laws Reduce Prescription Medication Use In Medicare Part D
Major finding:
Once a medical cannabis law is implemented, states see a drop in the use of prescription drugs for which medical cannabis can serve as an alternative.

When states implement legal medical cannabis programs, what happens to prescription drug use? To investigate this question, researchers used data on all prescriptions filled by Medicare Part D enrollees from 2010-2013. This allowed them to compare the number of doses prescribed per physician in states with medical cannabis laws compared to those without. Medicare Part D is the government program that subsidizes prescription drug costs for Americans aged 65 and older, so this study was limited to that segment of the American population.

They looked at the number of prescription drug doses filled out annually by doctors, and broke these down by the medical condition (pain, anxiety, nausea, etc.). For almost all conditions, states with medical cannabis laws saw doctors filling out fewer drug prescriptions compared to states without medical cannabis laws. As a key control analysis, researchers also looked at several classes of drugs for which medical cannabis is not thought to be useful. For these drugs, they observed no change in prescription rates following medical cannabis legalization.


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Which condition showed the largest decrease in prescriptions? By far, it was pain. On average, states with legal medical cannabis saw 1,826 fewer daily doses of prescription pain medications filled each year per physician. This is what you would expect if medical cannabis serves as an alternative or a supplement to traditional prescription pain medications. This observation also stands out given the ongoing opioid epidemic which is ravaging large parts of the country.

Medical cannabis may be a useful tool in the battle to curb opioid addiction, not only for its ability to help manage pain symptoms but also because of evidence that non-psychoactive cannabinoids like CBD have anti-addiction properties. The use of medical cannabis as an alternative to highly addictive prescription opioids is not viewed favorably by everyone, however. The pharmaceutical company Insys, which profits from the highly addictive opioid fentanyl, spent a lot of cash in the last election to help defeat cannabis legalization in Arizona.

Cannabis Study #3: Teen Use of Cannabis Has Not Increased; Use of Alcohol and Any Illicit Drug Other Than Marijuana at a New Low

Teen Use of Any Illicit Drug Other Than Marijuana at a New Low, Same True for Alcohol

Major finding: The percentage of teens using cannabis either dropped or held steady in 2016, depending on the age group. In fact, alcohol consumption and the use of other controlled substances are also on the decline.

This year’s annual Monitoring the Future survey, which surveyed ~45,000 U.S. teens, found that the use of cannabis, alcohol, and other illicit substances either held steady or decreased in 2016 compared to 2015. Cannabis use declined among 8th and 10th graders, and remained steady among 12th graders, in 2016. This observation directly contradicts the predictions that prohibitionists who have maintained that legalization will lead to increased consumption among teens. In response to these results, Dr. Nora Volkow, Director of the National Institute of Drug Abuse, told U.S. News: “I don’t have an explanation. This is somewhat surprising.”


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Cannabis Study #4: Are IQ and Educational Outcomes in Teenagers Related to Their Cannabis Use? A Prospective Cohort Study

Are IQ and Educational Outcomes in Teenagers Related to Their Cannabis Use? A Prospective Cohort Study

Major finding: This study failed to find an association between teen cannabis use and IQ or educational attainment after controlling for confounding variables, especially teen cigarette use.

Does cannabis use, particularly long-term use beginning in adolescence, have any long-term effects on cognition? Before this recent study, a couple of longitudinal studies in humans had examined this question, with the general conclusion being that regular cannabis consumption beginning in adolescence is associate with cognitive decline later in life.

However, these studies are tricky because adolescents who regularly use cannabis also tend to have higher rates of social adversity, early-age behavioral troubles, and to use other illicit substances. Because these things are all correlated with each other, it’s difficult to interpret results if you don’t carefully tease apart these potentially confounding variables.


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The recent study looked at the effects cannabis use on IQ and educational attainment. The data came from a large cohort (over 2,000) of adolescents in the UK who had been followed since their mother’s pregnancy. Importantly, researchers kept track of not only cannabis use, IQ, and educational scores over time, but also several other key factors. These included maternal and early-life factors (e.g. maternal education and mental health during pregnancy), childhood behavioral factors (e.g. conduct problems), childhood mental health (e.g. depressive and psychotic-like symptoms), and adolescent use of other illicit substances (including alcohol, tobacco, etc.).

Here’s the gist of what they found: without controlling for several confounding variables, you can find a negative association between cannabis use and educational outcome. In other words, adolescents who smoked “a lot” (50 or more times by age 15) saw lower IQ and educational attainments scores at age 15, compared to those who have never smoked. But when researchers controlled for the use of cigarettes, alcohol, or other controlled substances, this negative association was diminished. When they controlled for all of these things together, they actually found no statistically significant relationship between cannabis use and these measures.


Cannabis May Not Lower Your IQ, After All

Of all the potentially confounding variables they looked at, which one had the largest effect? It was cumulative cigarette use—how many times adolescents reported smoking cigarettes. Similar to cannabis use, cigarette use was negatively associated with IQ and educational attainment at age 15. However, unlike cannabis use, cigarette use remained negatively associated with these things even after controlling for those other variables. In fact, when researchers analyzed data only from those who had never smoked cannabis before, they found a significant negative association between cigarette use and IQ and educational attainment. Controlling for other variables diminished this association, but a significant negative association between cigarette use (in those who had never smoked cannabis) and educational performance remained.

Does this prove that it’s okay for teens to smoke cannabis if they avoid cigarettes, alcohol, or other substances? Absolutely not. There’s still plenty other evidence out there that regular use of cannabis, especially when it begins early in life, can affect brain development. It’s still possible that adolescent cannabis use may have an effect in ways that researchers could not measure here, or that heavy use by other adolescent populations could influence IQ or other measures. This study simply demonstrates why this type of research is so tricky, and why it’s critical to control for a variety of confounding variables.

Stay tuned in early 2017 for a deeper look at this and other important topics.


Ullman DF. The Effect of Medical Marijuana on Sickness Absence. Health Econ. 2016 [PDF]

Bradford AC, Bradford WD. Medical Marijuana Laws Reduce Prescription Medication Use In Medicare Part D. Health Aff (Millwood). 2016 [PDF]

Mokrysz C, Landy R, Gage SH, Munafò MR, Roiser JP, Curran HV. Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study. J Psychopharmacol (Oxford). 2016 [PDF]