Pubdate: Tue, 02 Feb 2016
Source: Seattle Times (WA)
Copyright: 2016 The Seattle Times Company
Author: Christopher Ingraham, The Washington Post


Research Report

Those Smoking Daily for at Least 5 Years Had Some Impairment

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

Professor Reto Auer of the University of Lausanne, Switzerland, 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 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 the words to the best of their ability.

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

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 as 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 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 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 heavily.

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.
- ---
MAP posted-by: Jay Bergstrom