UAB researchers have identified a link between diminished memory and marijuana use. (Photo from UAB News).
Mark Linn – Staff Writer
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A new research study at UAB suggests that long-term marijuana use can have a negative impact on verbal memory.
The findings were published as part of a recent survey conducted by a team of researchers that included Stefan Kertesz, M.D., an associate professor with the Division of Preventative Medicine and the study’s senior author.
“This is a hard question to study. In order to look for harms that are likely small, you need a very large number of people and you need to be able to have information about their use of drug or other substances over many years and you need to have some effort to measure an outcome over many years, preferably,” Kertesz said. “Usually studies that are actually funded to study drug abuse focus on small numbers and they usually focus on people with addiction.”
In order to obtain a sufficiently large sample population, the researchers used data from the Coronary Artery Risk Development in Young Adults study. The research began in 1985 with 5,115 participants aged 18 to 30 that were drawn from four cities across the U.S., including Birmingham. The researchers worked to include a base of people that varied by gender, race (white and African-American), age and education.
The seventh round of the study took place between 2005 and 2006 and involved 3,385 participants. As a part of the latest round, three tests of cognitive function were conducted as a part of the study. The first test tracked verbal memory, measuring the subjects’ ability to remember a series of words after about 25 minutes. The second measured how fast subjects could process information, and the third measured the subjects’ ability to complete tasks despite possible distractions, which is referred to as executive functioning and is associated with the frontal lobe of the brain.
Participants in the study who had smoked a significant amount of marijuana were found to have a slight impairment in verbal memory. For the purposes of the study, a “significant” amount of marijuana use was defined by a measurement the researchers referred to as “joint years.”
“Essentially, if somebody has reached a level equivalent to one joint a day for five years that would be called five joint years. You can reach that by smoking two joints a day for two and a half years, or five joints a day for one year, or half a joint a day for ten years,” Kertesz said. “I meant it could be any way you get to that. But in this study, people who reached that level had slightly worse ability to remember words in the word memory task.”
The subjects also performed slightly worse in the other cognitive tests, but those findings were not deemed to be statistically significant once adjusted for other factors such as health.
“The nature of our statistics makes it a little challenging to interpret into real English but one way to think about it is for every two people who accomplished five joint years of marijuana one of them will remember one word less on the task and the other one won’t be affected,” Kertesz said. “The size of this effect is small compared to what people consider a significant loss of cognitive function. “
The researcher said that the loss of cognitive function was roughly a quarter of what would be considered a significant loss of cognitive function experienced by some stroke victims.
“So this is not a study that says smoking marijuana makes you dumb,” Kertesz said. “It’s a study that says smoking marijuana interacts with the brain in these adults in a way that might be perceivable to some of them.”
Kertesz said that the test did not distinguish between different strains of marijuana. He also emphasized that since drug use tends to diminish with age, the majority of marijuana use by the study participants probably occurred in the 80’s and 90’s, and modern strains of marijuana tend to be more potent.
These findings come as marijuana use among college students is on the rise. A series of national surveys by the University of Michigan found that daily or near-daily marijuana use was reported by 5.9 percent of college students, the highest percentage recorded since study data became available in 1980. College students who reported using marijuana once or more during the last 30 days rose from 17 percent in 2006 to 21 percent in 2014. Use within the last year rose from 30 percent in 2006 to 34 percent in 2014.
This rise might be attributed to increased legalization and decriminalization, as well as greater acceptance of marijuana use. Fewer young people see marijuana as dangerous. Fifty five percent of 19 to 22 year old high school graduates viewed the use as dangerous in 2006, while only 36 percent viewed it as dangerous in 2014.
While many college students use marijuana recreationally, some use it as an alternative to prescription pills for issues such as chronic pain or anxiety.
“I primarily smoke it for its medicinal properties and for the calming effects it has on me. I suffer from anxiety and depression that I do not medicate with prescription pills, I see marijuana as my form of medication,” said a UAB International Relations major who wished to remain anonymous. “Its power to provide relief during or after an anxiety or panic attack is incredible, even as a preventative measure; it’ll stop an attack from happening before I can even start if I can feel it coming on.”
The student was not surprised by the findings of the study.
“Well, as mentioned, as far as providing anxiety relief, it’s a miracle drug. But when it comes to cognitive brain function and memory… yes, I will agree with the article that it truly does cause some wear and tear,” the student said. “By no means do I think it makes me ‘stupider’, however I can definitely tell a difference during simple moments, like trying to recall something from years ago or even just trying to recall something I did a few weekends before. However, when it comes to academics, I do not feel as though it effects [sic]me. I have never felt as though it has hindered my ability to comprehend or remember my materials.”
While the long-term effects on verbal memory appear to be small, Kertesz stressed that there are more significant effects of marijuana when used by people under the age of 22.
“So I think even if the percentage of individuals who will be affected is low, with the large number of people who are using marijuana recreationally, especially in states that have legalized, it there is going to be a significant number of young adults who will be harmed intellectually or educationally, or will develop an addiction,” the researcher said.
The researcher said he hoped to do more work in the future looking at comparisons between marijuana and other methods of treating chronic pain problems. He also hopes to see more research done on drug use in the larger population.
“What I would like to do is continue to support teams who are looking at drug use in general population adults so that we can help them make the best informed choice possible,” Kertesz said.
