Does Marijuana Cause Memory Loss?

August 29, 2017

Historically, movies and television -- more often than not -- portray cannabis users as being absent-minded, forgetful slackers. This stereotype has influenced many people's perspectives on weed and those who consume it. But, is this reality? Are people who consume cannabis more forgetful than those who abstain from it or is this merely a propaganda point popularized by anti-pot crusaders who want to obstruct legalization efforts?

Does Marijuana Cause Memory Loss?

Chemical Composition of Cannabis

In order to understand how cannabis affects memory, it is important to note that the cannabis plant contains many cannabinoids that affect individuals in a variety of ways.  THC and CBD are the two most prominent cannabinoids in cannabis with the greatest effects on consumers.

Cannabis doesn’t produce THC or CBD; instead, it synthesizes several cannabinoids that are activated -- usually by heat -- to yield the compounds of THC and CBD.


THC is the most psychoactive cannabinoid. (Psychoactive refers to substances that produce alterations in perception, mood, consciousness or behavior.) THC is the ingredient in cannabis that gives the user the feeling of being "high." CBD, on the other hand, is largely non-psychoactive.

Cannabinoids work by influencing the endocannabinoid system, specifically the brain and central nervous system.  THC gets its potent effect because it binds well with the Cannabinoid 1 receptor (known as CB1), while CBD exhibits low affinity for either CB1 or CB2 receptors. Instead, CBD acts as an indirect antagonist of these receptors.

Acute Memory

A study published in 2010 by the British Journal of Psychiatry tested 134 cannabis users on the effects of THC and CBD on their short-term memory.  The participants were given memory tests before and after they had smoked cannabis.

The percentage of THC in the plant were similar among all users, so the groups were split up based on the percentage of CBD. The results showed that the group that had smoked a high THC percentage and a low CBD percentage were more likely to have short-term memory impairment than those who smoked cannabis with higher CBD content.  Additionally, the author of the study noted that the high CBD group’s performance on the memory tests was nearly indistinguishable from their pre-drug tests.


Other studies have found that prolonged and chronic use of high-THC marijuana can produce adverse (although reversible) cognitive effects on memory. (And, even lower IQ in some habitual users who start using in adolescence.) While these studies are notable, it's important to note that little research has considered CBD's potentially attenuating effects of THC. Translation: CBD appears to act like THC's responsible sibling, minimizing THC's negative effects. Moreover, few studies consider how varying levels of THC may affect users differently.

Think about it this way: should all alcohol be lumped into one group while being studied?  Someone who consumes 24 ounces of 80-proof (40%) hard liquor per day is likely to show different symptoms than someone who drinks 24 ounces of a 5% beer per day.

Varying percentages of THC and CBD have been shown to cause different effects on an individual, much like the percentage of alcohol in adult beverages influences its effects.

Understanding the difference between THC and CBD is of great importance to any cannabis consumer.  Though more research is needed to understand marijuana's effects on memory better, early studies suggest that a high CBD percentage strain is the way to go if you are concerned about potential memory impairment.  `

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