According to a recent study by Deborah Levine, an assistant professor at the University of Michigan Medical School, long-term marijuana use is associated with poor verbal memory in middle age.
Levine, who is an investigator of risk development in coronary arteries for young adults, practices at both the University Hospital and VA Ann Arbor Healthcare System.
Levine, along with Reto Auer, a researcher at the University of Lausanne, Switzerland, compiled data from a 25-year CARDIA study, which analyzed cognitive performance by observing and calculating the verbal memory, executive function and processing speed of participants.
According to Levine, there seemed to only be a correlation between marijuana usage and verbal memory, with no evidence of an effect on processing speed or executive function.
However, Levine emphasised that correlation is not equivalent to causation.
“Our results found a significant association between long-term marijuana use in early adulthood and decreased cognitive functioning at midlife,” Levine said. “However, our results demonstrate an association and do not prove causality.”
With large numbers of adolescent and young-adult marijuana users and an ongoing movement to decriminalize and legalize marijuana, Levine said the issue of the health effects of marijuana is relevant. States have legalized marijuana, and many cities including Ann Arbor have decriminalized its meaning. According to the 2013 National Survey on Drug Use and Health (NSDUH), marijuana is the most commonly used illicit drug, with a total of 19.8 million past-month users in the United States.
“I hope that current and potential users will consider the potential long-term effects of marijuana use on their brain health, particularly their cognitive functioning when deciding to use or not to use,” Levine said.
In an interview, LSA sophomore Jason, who smokes marijuana regularly and requested to be referred to by only his first name, said the results of the study do not impact his perceptions on marijuana use.
“I really don’t see marijuana as a serious risk to my health short- or long-term,” Jason said. “It may affect my ability to remember a given list of words, according to one specific study, but ultimately I don’t see it as a barrier to my overall success in life or health overall.”
There were 3,385 participants, 84.3 percent of whom reported marijuana use and 11.6 percent of whom continued to use marijuana into middle age. From the data, Levine concluded that an average of one out of two participants remembered one fewer word from a list of 15 words, for every five years of past exposure to marijuana.
Levine said that this statistic is significant, but the investigation of the effects of marijuana consumption on cognitive function is ongoing.
“Additional research would be needed to demonstrate the clinical effects of decreased verbal memory in individual day to day functioning,” Levine said.
It still remains unknown as to whether occasional or low-intensity marijuana use earlier in life has long-term effects, and whether factors such as age and duration of exposure have to be taken into account.
Jason said he did not believe verbal memory loss was a life-threatening issue.
“I haven’t looked too far into the research,” Jason said. “But verbal memory isn’t threatening to my life and I assume that I’ll slow down my consumption of marijuana over the course of my life.”
Self-reporting was utilized to assess the results of the study, which is sometimes considered a less reliable method of study, but Levine said this was not a primary issue for the research team.
“Self-report of marijuana use is the gold standard and customary approach for measuring an individual’s marijuana use,” Levine said. “I do not feel that it is a major limitation.”