Pubdate: Tue, 02 Feb 2016
Source: Albuquerque Journal (NM)
Copyright: 2016 Albuquerque Journal
Author: Christopher Ingraham, the Washington Post


Research Also Found No Effects on Focus or Problem-Solving

New research published Monday in the journal JAMA Internal Medicine
confirms what many of us have suspected for some time: If you smoke a
lot of weed - like a lot of it - it can potentially do permanent
damage to your short-term memory.

Professor Reto Auer of the University of Lausanne led a team of
researchers who examined data on the marijuana habits of nearly 3,400
Americans over a 25-year period. At the end of the study period, the
subjects took a battery of tests designed to assess cognitive
abilities - memory, focus, ability to make quick decisions, etc.

The study found that people who smoked marijuana on a daily basis for
a long period of time - five years or more - had poorer verbal memory
in middle age than people who didn't smoke, or who smoked less. This
association remained even after researchers controlled for a variety
of other factors known to affect cognitive performance - such as age,
education, use of other substances and depression.

Auer and his team measured lifetime marijuana exposure in a fantastic
new unit of measurement they call "marijuana-years." Essentially, if
you smoke pot every day for a year, that equals one marijuana-year of
use. Ditto if you smoke every other day for two years, or once a week
for seven years.

The relationship between marijuana exposure and memory problems was
essentially linear. The more pot people smoked, the worse they
performed on the memory tests. But just how much worse?

Let's say we have two groups of 10 people each. You tell each of them
a list of 15 words and ask them to memorize them. Then, 25 minutes
later, you ask them to recall all of the words to the best of their

The first group consists of 10 people who don't smoke pot or do so
only occasionally. Let's say, on average, people in this group would
be able to remember nine of the 15 words.

The second group consists of people who smoked pot every single day
over a period of five years. On average, they'd be able to recall 8.5
of the 15 words.

That doesn't seem like a huge cognitive difference and, by and large,
it's not. But multiply that by every five marijuana-years of exposure
and the gap can start to get larger. For instance, say you had a group
of people who smoked weed literally every single day from age 20 until
they turned 45. At age 45, you'd expect these folks to remember, on
average, 2.5 fewer words than a comparable group who had smoked
occasionally or not at all over the same period.

Few people actually smoke this much pot. Among the 3,385 study
subjects, only 311 (8 percent) had more than five marijuana-years of
exposure. But many drug policy experts are concerned that legalizing
marijuana and making it easier to get will cause rates of heavy,
problematic use like this to rise.

One important caveat is that a study like this can't determine
causality. It could be the case that heavy pot use makes your
short-term memory bad, or it could be that people who operate at a
lower level of cognitive function are more inclined to use marijuana

It's also worth noting that the other cognitive abilities researchers
tested - focus and processing speed - did not seem to be significantly
impacted by heavy marijuana use.

The association between short-term memory declines - potentially
permanent ones - and heavy pot use is very real, according to this
study, and shouldn't be discounted. On the other hand, it's also quite
surprising that you can smoke weed literally every single day for five
years and not have it impact your problem-solving abilities or your
ability to focus at all.

These findings also need to be understood in relation to what we know
about the severe cognitive effects of persistent, heavy alcohol use,
which include irreversible brain damage.

Overall, the take-home message is one of moderation. Whether your
preferred vice is pot or alcohol or gambling or Big Macs, it stands to
reason that, if you overdo it, you're going to hurt yourself.
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