Alex Berenson’s new book had a brief moment in the sun earlier this year, with favorable coverage in Mother Jones, a cordial review by Malcolm Gladwell in The New Yorker, and an essay from Berenson promoting the book in the New York Times,
before being shouted down by a chorus of online critics. The critics
had a point: This is a book that aims to marshal reams of statistical
evidence documenting a link between marijuana and psychosis — and in
turn one between marijuana and violence — and Berenson, to put it
bluntly, is not particularly skilled when it comes to evaluating such
evidence.
And yet, though he vastly overstates it, Berenson has a point too: There are signs that marijuana use can
cause both temporary psychosis and full-blown schizophrenia, and we
need to study this possibility as states debate whether and how to
decriminalize or legalize the substance. We may ultimately decide that
the risks of smoking pot are not serious enough to justify interfering
in people’s personal decisions, much less incarcerating them. Indeed, on
the basis of what we know now, that is my own view. But for all its
flaws, Tell Your Children forces us to confront the idea that weed might not be as harmless as we think.
Ultimately, establishing marijuana’s
connection to psychosis and violence boils down to the age-old quandary
of how to distinguish causation from mere correlation. That there is a correlation
between pot use and these bad outcomes is well established: Pot users,
especially the heaviest users, are more likely to be schizophrenic or
violent than non users. But the question of whether these relationships
are causal is far trickier.
In a comprehensive and carefully written
2017 report reviewing the evidence on marijuana’s health effects, the
National Academy of Medicine noted that when substance use and mental
illness overlap, there can be three different reasons: 1) Substance use
changes the brain in ways that cause mental illness; 2) mental illness
causes people to use substances (say, to self-medicate); and 3) there
are environmental or genetic influences that predispose people to both
substance use and mental illness. “Although the precise
explanation is still unclear,” the authors wrote, “it is reasonable to
assume” that the reality is a mixture of these. In true academic form,
the authors then called for more research to untangle this knot.
On the specific issue of pot and
psychosis, while the report is quite confident in the correlation
between the two, it rarely uses causal language and hedges when it does.
For example: “Cannabis use is likely to increase the risk of
developing schizophrenia and other psychoses” (emphasis mine).
The
authors also note that while pot use predicts the future
development of psychosis — indicating that self-medication among the
mentally ill isn’t the whole story — it’s also true that some societies
have seen marijuana introduced to them without experiencing an increase
in psychosis. In other words, while pot may indeed increase the risk of
psychosis, we’re not quite sure it does, much less to what degree. And
the degree is important too: A common estimate is that 1 percent of the
population has schizophrenia, for example, and there’s a big difference
between marijuana’s increasing that risk to 1.1 percent and increasing it to, say, 3 percent.
Berenson takes all that hedging and
nuance and chucks it out the window at some stoner minding his own
business on the sidewalk. An entire section of the book is called
“Proof”; one chapter is entitled “Study after Study after Study.” And
no, he doesn’t have access to some groundbreaking new scientific
technique that justifies such confidence.
A good illustration of the problem is a piece of research published in The Lancet
in 1987, a seminal work that Berenson quite rightly puts under the
spotlight for several pages. Using a massive data set on Swedish
military conscripts, it found that people who’d used pot at least 50
times were at six times the risk of developing schizophrenia of those
who’d never used. It also found that the relationship persisted after
adjusting for assorted control variables such as conscripts’
socioeconomic status and whether their parents were divorced.
But that’s not the end of the story.
Among those who’d used ten times or more, the “relative risk” fell from
about 4.6 to 2.3 times higher when the control variables were added.
(The study does not report these results for the 50-times-plus group
alone.) And while the remaining 2.3-fold difference might be there
because pot really does cause schizophrenia, it also might be there
because the control variables are inadequate. Asking someone whether any
family members take medication for “nervous problems” (another variable
from the study) is not the same as accounting for that person’s full
genetic makeup; there is also no way to measure every relevant aspect of
a person’s environment.
Even some of the variables that are
measured are not measured perfectly, because they are based on
self-reports — and a variable measured with error can’t truly “control”
the thing it represents.
We just don’t know whether all, none, or
some — and if some, how much — of that 2.3-fold increase is the result
of pot causing schizophrenia. And the fact that the relative risk falls
so dramatically with controls is highly troubling, because it indicates
that there’s a lot of statistical “confounding” in what we can measure.
Admirably, Berenson discusses the various
limitations of the study. But then he just carries on, piling up more
research that suffers from similar problems and arrives at similar
conclusions and pretending it solves something. A whole lot of the
studies he cites follow the same script: There’s a correlation between
weed-smoking and either psychosis or violence; it doesn’t go away (but
does shrink) when the researchers toss some control variables into the
mix; this is treated as serious evidence of a causal relationship, with a
caveat here and there but also strident assertions from Berenson that
the pathway from pot to these bad outcomes is definitively established.
And this pattern is even more grating with violence than it is with
schizophrenia. People with criminal tendencies are more likely to do
drugs?
Who knew?
Berenson’s effort to analyze the issue
geographically fares no better. Much of the online backlash earlier this
year, for example, involved his claim that between 2013 and 2017, the
four states that legalized recreational pot all saw above-average
increases in violence. In his defense, it is a bit odd that all
four pot states saw this. But this analysis is an incredibly crude
exercise, especially since these four states implemented their laws at
different points during this period, and it flies in the face of the
fact that crime has generally fallen as pot use among young men, our
most violent subpopulation, has ticked up since the turn of the century.
What’s particularly frustrating is that
elsewhere in the book, Berenson has a professor friend run a more
sophisticated analysis of geographic trends in opioid deaths as they
relate to medical-marijuana laws and to marijuana use as measured by
surveys; a study had claimed that medical-marijuana laws reduce opioid
overdoses, but Berenson’s friend adds more data (as the original study
ended with 2010) and finds no effect. You can do the same type of thing
with crime rates, but there’s no such analysis to be found here. The
same goes for the little-noticed but alarming recent upticks in “serious
mental illness” in surveys and psychosis cases at hospitals that
Berenson notes: Were they concentrated in states that legalized pot or
saw particularly large increases in illegal use? The data exist, but
Berenson doesn’t have his friend crunch them.
Maybe the idea came too late in the
process. Berenson’s uncompensated research assistant, a
political-science and law prof at New York University, gives a “long
pause” after one request and our favorite buzzkillin’ journalist
realizes he’s out of favors.
To do this topic justice, Berenson didn’t
just need a numerate friend willing to donate some time; he needed a
co-author or at least a paid helper who specializes in drug policy:
someone familiar with the quirks of the relevant data, willing to run
new analyses, and able to help him assess the various studies he writes
about. He also needed footnotes citing all of the studies he refers to,
and an appendix with the full methodology and results of the original
analyses. Then again, if he’d done all that, he’d have written something
a lot more similar to the aforementioned National Academy of Medicine
report.
When we look to the future, other lines
of evidence are rapidly emerging and could provide stronger answers.
Berenson discusses a sophisticated technique called “Mendelian
randomization” inaccurately, briefly, and vaguely. (He claims a study
“rule[s] out” a genetic explanation for the marijuana–schizophrenia link
despite the fact that different studies have reached different
conclusions, and thanks to the lack of footnotes I’m not even sure which
study of several in this vein he’s referring to.) To oversimplify, the
technique involves looking to see whether people with genes for
schizophrenia are more likely to use pot and whether people with genes
for pot use are more likely to develop schizophrenia and trying to infer
a causal relationship from there. Some early results suggest the effect
might go both ways — i.e., schizophrenia causes pot use and pot
use causes schizophrenia — but there’s much work left to be done,
including figuring out which genes even to take into account in such
analyses.
So where does this leave us? Berenson
thinks it obvious that legalizing pot is a bad idea. As someone who
changed his mind in the wake of the opioid epidemic about
across-the-board drug legalization, I ought to be at least somewhat
sympathetic. I am not. Easily available opioids set off an epidemic that
killed nearly 48,000 Americans in 2017, almost triple the number who
died by homicide of any kind; marijuana, by contrast, may increase the
risk of schizophrenia from 1 percent or so to some higher number in
heavy users, and also may occasionally trigger violent episodes (though
in other cases one imagines it might prevent violent episodes through its more typical effect of mellowing users out).
You can tell your children not to smoke
pot on the basis of these risks, certainly, and punish people who drive
while high, get aggressive when they smoke, provide pot to minors, or
switch to hard drugs such as cocaine. Reasonable people might even argue
for a strictly limited form of legalization (as Jonathan Caulkins has
in this magazine), or at least to tax marijuana heavily or regulate its
potency. But to my mind this is simply not worth trampling on personal
freedom over. Smoking marijuana is well within the range of risks we
should allow adults to take.
I can’t recommend you read Tell Your Children;
the National Academy of Medicine report, available for free online,
provides a far more balanced and scientifically rigorous summary of the
mental-health effects of pot. It must be said, however, that with his
more, ahem, aggressive approach, Berenson has drawn attention to a
significant potential risk of marijuana abuse, one that deserves close
study and careful monitoring as pot laws inevitably continue to loosen.
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