A new study published Monday confirms smoking weed on a daily basis can potentially cause permanent damage to your short-term memory.
The study, published in the journal JAMA Internal Medicine, followed the marijuana usage of nearly 3,400 Americans, examining their cognitive ability at the end of a 25-year period, The Washington Post reports. Professor Reto Auer and his team of researchers from Lausanne University in Switzerland tested the participants’ performance in memory, processing speed and ability to make decisions.
It was found that those who smoked pot on a daily basis for at least five years were associated with worse verbal memory when compared to people who smoked infrequently or not at all. This study controlled for variables that could impair performance, such as age and education level, and excluded participants who were currently intoxicated.
To measure lifetime marijuana usage, the research team defined a new unit know as the “marijuana year.” Under their definition, smoking pot every day for a year adds up to one marijuana year, whereas smoking pot every other day for two years also adds up to one marijuana year.
This study found a linear relationship between marijuana usage and the worsening performance in verbal memory tests.
“After excluding current users and adjusting for potential confounders, cumulative lifetime exposure to marijuana remained significantly associated with worse verbal memory,” the study reports.
To put these results into perspective, compare two groups of people who are both shown a list of 15 words and asked to recall the information after 25 minutes. The first group of people, who smoke pot occasionally or not at all, could remember 9 out of 15 words. The second group, who smoke everyday for an equivalent of five marijuana years, could remember 8.5 out of 15 words.
This may not seem like much of a difference until you consider the long-term results. If you extend the period from five to 25 years of daily usage, you would expect to see the consistent users to remember 6.5 words out of 15 when performing the same test. These results could prove to be problematic for middle-aged adults.
With increased talks of marijuana legalization across the United States, this problem could continue to grow. The study points out that most people do not smoke this much weed on a daily basis — only 8 percent of the study participants did — but that percentage could rise with increased legalization.
Although these results do not prove causality, whether the loss in memory is caused by marijuana or people with lower cognitive function are more inclined to smoke pot, they do leave us with a warning: Marijuana is best enjoyed in moderation.