A long term marijuana study! According to a paper published in the journal JAMA Internal Medicine, long term marijuana users may suffer a decrease in verbal memory as they reach middle age.
The landmark study also shows that processing speed and executive function do not appear to be affected by marijuana use.
The extensive research started all the way back in 1985 thanks to participants of the Coronary Artery Risk Development in Young Adults (CARDIA) study. Subjects were surveyed, and subsequently interviewed about their marijuana use after 2, 5, 7, 10, 15, 20 and 25 years, before being asked to undertake a series of cognitive assessments in 2011.
Out of 3,385 participants, 11.6 percent said they continued marijuana use into their mid life. Out of this cohort, there was a clear distinction between the results of marijuana users and non-users of the Rey Auditory Verbal Learning Test, which assesses verbal memory.
The test asks participants to memorize a list of 15 words. Results suggest for every 5 years of marijuana use, subjects were found to have a 1 in 2 chance of being able to remember one word fewer from the list of 15 words.
Other tests were used to assess processing speed and executive function. No link was discovered between marijuana use and cognitive performance in these two categories.
Researchers say it’s possible marijuana may affect the brain’s hippocampus, which is responsible for memory and learning, although the exact process of how this happens is unknown. Other studies have suggested this link as well.
The team hopes the study will be used by policymakers to educate the public on the affects of long term marijuana use, being that there are not many comprehensive, long term cannabis studies out there.