Does Using Drugs ‘Even Just Once’ Change Your Brain Forever?

Last Friday Live Science reported
the results of an unpublished study finding that “teens who have
used drugs even just once in their lives have brain characteristics
that are different from those who have never used drugs.” That is
the sort of finding that resulted in a
mini pot panic a few months ago, after a study reported
in The Journal of Neuroscience supposedly found
that “marijuana re-shapes brains of users” (according
to NBC
News), that “even casually smoking marijuana can change your
brain” (per The
Washington Post), that “casual pot use impacts brains
of young adults” (The
Oregonian), that “recreational pot use” is “harmful to
young people’s brains” (Time),
that “casual marijuana use” is “bad for young adults”
(The
Times of India), and that “even ‘casual’ marijuana
use can knacker bits of your brain” (Gizmodo
UK).

In both cases, the brain differences were measured by MRI scans
at a single point in time, so it is impossible to say whether they
were caused by drug use. It also is not clear whether the
differences are permanent or, most important, whether they have any
functional significance. But so far the newer study has not
generated the same sort of sensational coverage (although that
might still happen), possibly because the lead researcher,
University of California at Davis graduate student David G.
Weissman, says his findings probably reflect pre-existing
differences among his subjects.

Here is how Live Science describes the results of
Weissman’s study, which involved 71 Mexican-American
16-year-olds:

Among teens who’d ever used drugs, a brain region known as the
nucleus accumbens—which is thought to play a role in
the rewarding feeling that can come with taking drugs—was more
in sync with areas of the brain in the prefrontal cortex, compared
to in teens who’d never used drugs. The prefrontal cortex is
involved in decision making, planning and other behaviors that
require complex thinking.

But the nucleus accumbens was less in sync with an area near the
hippocampus, which is important for memory formation, in
teens who had used drugs, compared with those who had never
used. 

Weissman thinks these differences, rather than resulting from
drug use, made the subjects more inclined to use drugs:

Weissman said he suspects that these brain differences existed
before drug use, and underlie a tendency to take risks, which
includes using drugs, he said.

Weissman said the level of drug use among the teens in the study
was typical of teens that age —about half had used drugs before,
and they did not use drugs very frequently.

“It’s possible, but seems unlikely, that that level of use would
produce significant changes [in the brain], but it’s an open
question,” Weissman said.

Whichever direction the causality runs, making a big deal of
Weissman’s findings seems unwarranted. Among older teenagers, drug
use is not aberrant; it is normal. Since survey
data indicate that most Americans have consumed drugs (most
commonly alcohol, tobacco, and/or marijuana) by the time they turn
16, perhaps it is abstinence that requires an explanation.

[Thanks to Ron Steiner for the tip.]