A new paper from Hasin and colleagues at JAMA Psychiatry reviews data:
from NESARC and from the National Institute on Alcohol Abuse and Alcoholism
2012-2013 National Epidemiologic Survey on Alcohol and Related Conditions–III (NESARC-III), a survey of 36,309 new participants.
The NESARC field procedureswere similar to those in NESARC-III.
There are really three key observations, although the tables also break down the findings by sex, age, race/ethnicity, education level, etc.
First, past year use of marijuana went from 4.1% to 9.5% of the sampled populations. Interesting, but hey, could just be more people feeling free to try it out, right?
Second finding looked at prevalence of meeting DSM-IV criteria for a Marijuana Use Disorder (including Abuse and Dependence subcategories) in the past year. This measure went from 1.5% to 2.9% of the population.
The third finding is that if you condition only upon those individuals who have tried marijuana at least once in the past year, the rate of a Marijuana Use Disorder went from 35.6% to 30.6%.
This is all relevant to a few themes we've discussed before on the blog.
I don't see how you can view these data other than in a context of growing liberalization of medical marijuana laws and availability of marijuana. This refutes the occasional position struck by the pot fans that changes in legal status and attitude won't change use rates because everyone who wants to smoke marijuana already does. Clearly the US population undergoes significant changes in exposure to marijuana. In this case only over a decade.
My position has also been that, in general, as you increase the number of people who are exposed to a given drug you are going to see an increase in problems related to that drug. In the absence of other information, we must start our estimate of that rate from what we observe at a given time. The first two numbers in the study confirm this. As use rates increased, so did rates of meeting criteria for DSM-IV diagnosis of a MUD.
The conditional probability measure also addresses this phenomenon, perhaps in an even better way. I have mentioned before that it is really hard to assess conditional probability of dependence between drugs that feature significant base-rate exposure differences. You can't help but assume there is going to be a curve whereby the more democratic the exposure, the larger will be the occasional user population. That is, I assume some sort of nonlinearity is going to occur against the general estimation I mention above. I presume the lower the incidence of exposure to a given drug, perhaps the higher the conditional probability of dependence and the higher the incidence of exposure, the lower the conditional probability.
In this case, I'd say the change in conditional probability is not that significant. Something around a third of those who smoke marijuana in a given year are meeting criteria for a MUD across a doubling of the incidence of exposure. The curve is still pretty linear although I assume we will be getting another jump in a decade and can see how this curve shapes up.
This estimate of a MUD is really high to my eye, no doubt because it includes abuse and dependence together. Perhaps the data I usually think about (7-9% dependence rate) references dependence without abuse...I have to go check on that. In case you are wondering, the difference really boils down to symptoms of tolerance (diminished effect at same dose, increasing dose to get desired effect) and withdrawal, as well as some indicators of uncontrolled use relative to a person's intentions.
Now interestingly the authors reference another similar study (NSDUH) that didn't find an increase in prevalence that was so large- only 12% reported by Pacek et al, 2015. The present authors suggest more detailed questioning in the NESARC approach may explain the difference.