Pubdate: Mon, 01 Jul 2013
Source: Wall Street Journal (US)
Copyright: 2013 Dow Jones & Company, Inc.
Author: Samuel T. Wilkinson


Medical research shows a clear link between marijuana use and mental

Recent legislation has permitted the recreational use of marijuana in
Colorado and Washington state. Those who support legalization often
tout the lack of serious medical consequences associated with the
drug. Most of us know people who used marijuana in high school or
college and seem to have suffered no significant medical consequences.
As the medical and scientific literature continues to accumulate,
however, it is becoming clearer that the claim that marijuana is
medically harmless is false.

There is a significant and consistent relationship between marijuana
use and the development of schizophrenia and related disorders.
Schizophrenia is considered by psychiatrists to be the most
devastating of mental illnesses. Patients who suffer from it often
experience auditory or visual hallucinations, severe social withdrawal
and cognitive impairment. Many require frequent and prolonged
hospitalization in psychiatric wards.

Schizophrenia affects almost three million Americansa=C2=80"more than six

times the number of people with multiple sclerosis, two and a half
times the number of people with Parkinson's disease, and more than
twice the number of people with HIV/AIDS. Less than one-third of
patients with schizophrenia can hold a steady job or live
independently. A large portion (about one-third) of homeless people in
the U.S. suffer from the disease.

Though they receive little attention in the legalization debate, the
scientific studies showing an association between marijuana use and
schizophrenia and other disorders are alarming. A 2004 article in the
highly respected British Journal of Psychiatry reviewed four large
studies, all of which showed a significant and consistent association
between consumption of marijuana (mostly during teenage years or early
20s) and the later development of schizophrenia. The review concluded
that marijuana is a "causal component," among others, in the
development of schizophrenia and other psychotic disorders.

A 2007 study in the Lancet, a British medical journal, concludes that
using marijuana increases the risk of young people developing a
psychotic illness, such as schizophrenia. This risk is greatesta=C2=80"up

to a 200% increasea=C2=80"among those who use marijuana heavily and who
start using at a younger age.

Those not familiar with epidemiological causation may wonder how
cannabis could "cause" schizophrenia if so many people who smoke
marijuana or hashish don't develop the disease. As an example, medical
researchers have known for several decades that smoking causes lung
cancer, yet over 80% of smokers do not develop lung cancer.

As research accumulates, the emerging picture is that marijuana
precipitates schizophrenia or related psychotic disorders in people
whose brains are inherently vulnerable to psychosis. All of us who do
not regularly experience hallucinations or delusions reside on what
may be called a "cliff of sanity." Some of us, for reasons still
unclear (thought possibly to be genetic), are closer to the edge of
the cliff than others.

Marijuana may push everyone a few feet closer to that cliff. For those
who were already close to the cliff, the drug pushes them over the
edge into the chasm of insanity, hence precipitating the development
of schizophrenia.

The association between schizophrenia and marijuana is not the only
issue at play in the debate over marijuana legalization. If
legalization is certain to decrease the power of drug lords in Mexico
and other countries, then this is certainly a favorable outcome.
However, if the trade-off is that more people suffer from
schizophreniaa=C2=80"and thus more Americans are homeless and
debilitateda=C2=80"then this must be recognized and discussed by the
general public. This association between marijuana and serious and
devastating psychotic disorders has been absent or under-recognized in
the public debate.

Despite (or perhaps because of) the unwarranted stigma that surrounds
their illness, individuals with schizophrenia are vulnerable and in
need of advocacy. We owe it to them, and to society in general, to
consider all the facts, risks and potential benefits before we embark
on this drastic social experiment. If the end of Prohibition offers
any historical precedent, once marijuana is legalized it will be all
but impossible to undo.

Dr. Wilkinson is a resident physician in the Department of Psychiatry
at The Yale School of Medicine. His opinions do not necessarily
reflect those of The Yale School of Medicine or its Department of

A version of this article appeared July 2, 2013, on page A13 in the
U.S. edition of The Wall Street Journal, with the headline:
Pot-Smoking And the Schizophrenia Connection.
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