Cannabis and Memory Loss

People who smoke cannabis can risk the possibility of memory loss, particularly when ‘high’ on the drug. Concerns exist over long term memory loss following use of marijuana. Whether this is possible may depend on many factors including length of use and impact on the individual’s brain.


Marijuana and the Brain

The main active chemical in marijuana is Tetrahydrocannabinol (THC). THC passes from the lungs into the bloodstream which then carries it to the brain and other organs throughout the body. The half life of THC is approximately 3-4 days. When THC is active in the brain (1-6 hours after ingestion), THC impacts cannabinoid receptors and triggers a series of cellular reactions. Two main receptors for cannabinoids, CB1 (in the brain) and CB2 (in the spleen) are affected by ingestion of marijuana. The CB1 receptors, when stimulated, produce both euphoria along with impaired short term memory and sense of time.


Memory Loss

Four reasons have been identified as to why memory loss occurs with marijuana use. One theory is the cognitive effects related to memory loss are due to a reduction in blood flow to the brain. Other researchers believe memory impairment occurs when THC impacts the hippocampus (responsible for converting information into short term memory). THC alters how information is processed by changing the way sensory information is processed. New information is not able to be processed by the hippocampus for this reason. Other issues which occur include:

  • THC creates changes to structure of hippocampus region of the brain
  • New information cannot be retrieved for longer than a few minutes
  • A decrease in nerve cell activity occurs with marijuana use


Long Term Memory

The long term effects of marijuana use are less studied than short term effects. Marijuana negatively impacts learning and memory in chronic daily users with adverse effects lasting days or weeks after effects of drug have worn off. A person who smokes marijuana every day may, indeed, function at a suboptimal intellectual level on a consistent basis.



The THC in marijuana can interrupt the brain’s ability to process and retain new information. Long term effects of marijuana on memory have yet to be studied. Chronic marijuana use is not studied as thoroughly as short term use so it is imperative to pay attention to any changes in the ability to focus, concentrate and retain information if there are concerns about memory loss. Overall, it may be helpful to speak to a doctor about any concerns an individual has about memory loss.

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