New Studies on Memory and Marijuana usage.

Research shows that marijuana use affects short term memory, but how does it also affect Long Term Memory. How are short and Long Term memories are related. STM holds a small amount of information for a short amount of time. STM is processed in one of two ways, maintenance rehearsal and elaborative rehearsal. Elaborative rehearsal works better when transferring memories into LTM. Elaborative rehearsal is when you relate the information in STM to information you already have stored in LTM. Elaborative rehearsal works because we are processing the information on a deeper level. So in order to form LTM we must first be able to form STMs. How does the use of marijuana affect this process?
According to International weekly journal of science the THC in marijuana weakens the connections, or synapses, between neurons in the hippocampus. The hippocampus is a structure in the Medial Temporal lobe that is crucial for forming new LTMs. This was shown in a case where a person’s hippocampus’ were removed from both sides of the brain to eliminate epileptic seizures but also eliminated their ability to form new LTMs. Smoking marijuana is not as drastic as removing the hippocampus but because the hippocampus contains a lot of THC receptors it does affect the ability to form new LTMs. By the weakening of the connections in the hippocampus memory function is slowed down or stopped in Short and long term memory while on the substance.
Although the memory process is slowed down while using marijuana until recently long term affects affecting memory had not been seen. A study was done on teens who were using marijuana on a daily basis. The people in the study had started using marijuana between the ages of 16 and 17 and used it daily for 3 years. At the time of the study they had been marijuana free for two years. These participants performed 18% worse on long-term memory tests than young adults who had never used cannabis on a long term daily basis. These same participants who scored 18% less also had abnormally shaped hippocampus’. This is one of the first studies to show that correlation between long term memory problems and abnormally shaped hippocampus.
Marijuana is shown now to affect both short and long term memory. Although studies are just starting to be completed and further studies are starting up all over the globe. It is exciting to see what more we can learn about ourselves and the world around us.
Smith, M. J., Cobia, D. J., Reilly, J. L., Gilman, J. M., Roberts, A. G., Alpert, K. I., Wang, L., Breiter, H. C. and Csernansky, J. G. (2015), Cannabis-related episodic memory deficits and hippocampal morphological differences in healthy individuals and schizophrenia subjects. Hippocampus, 25: 1042–1051. doi: 10.1002/hipo.22427

HOW DOES MARIJUANA AFFECT THE BRAIN? (n.d.). Retrieved December 1, 2015, from
(n.d.). Retrieved December 1, 2015, from

4 thoughts on “New Studies on Memory and Marijuana usage.

  1. Giulianni Hardy-gerena

    After reading your post, I wondered what effects (if any) marijuana had on users who started smoking as adults or who smoke occasionally (as opposed to being dependent). The warnings that I read in your post reminded me of the familiar warnings communicated about teens and alcohol abuse. After doing a little digging, I realized there is relatively little research on the effects of occasional marijuana or adult initiation. I think the conversation on marijuana would benefit a bit more nuance.

    A few years ago, The Substance Abuse and Mental Health Services Administration (SAMHSA), published a report highlighting the negative effects associated with marijuana abuse, including impaired short-term memory. However, an analysis of substance abuse treatment admissions between 2000 and 2010 revealed that nearly nine out of ten clients reported using marijuana before age 17. The report also found that adult initiates used a smaller variety of substances and smoked marijuana for a shorter duration of time (“Report Compares Early Marijuana Initiation with Adult Initiation,” 2013). These findings suggest that age of initiation is a critical factor in the determining the risk of abuse in marijuana users.

    During my research, I also found an article published in the Journal of Neuroscience that claimed that even occasional use of marijuana could alter brain structure. The results of the experiment were interpreted by its authors as an indication that all marijuana use posed a potential threat to normal cognitive functioning (Gilman et al., 2014). However, several scientists, including Dr. Pachter from the University of California, Berkeley, identified several flaws in the study. There are two flaws that are relevant here: 1) Most of the “occasional” users in the participant pool smoked more than 10 joints per week and 2) the experimental design only suggests a correlation and not a cause-and-effect relationship between altered brain structure and marijuana use (Pachter, 2014). It is not clear from this study if someone who smokes once or twice a week would present with the same changes in brain structure. More importantly, even if a once- or twice-a-week smoker did present with the same changes, additional research would be needed to determine if the differences in brain structure caused the smoking or if smoking caused those changes.


    Gilman, J. M., Kuster, J. K., Lee, S., Lee, M. J., Kim, B. W., Makris, N., . . . Breiter, H. C. (2014). Cannabis Use Is Quantitatively Associated with Nucleus Accumbens and Amygdala Abnormalities in Young Adult Recreational Users. Journal of Neuroscience, 34(16), 5529-5538. doi:10.1523/jneurosci.4745-13.2014

    Pachter, L. (2014, April 17). Does researching casual marijuana use cause brain abnormalities? [Web log post]. Retrieved from

    Report compares early marijuana initiation with adult initiation. (2013, October 02). Retrieved from

  2. Graciela Rosita Pulido

    Blog Comment #3
    New Studies on Memory and Marijuana Usage
    Jennifer, your blog New Studies on Memory and Marijuana Usage was very well-written. The way you expressed how the new information that is becoming available in the substance use of marijuana was interesting. I enjoyed how your research for the topic highlighted the distinct difference between how STM affects LTM and vice versa. I was reading an article published in the New York Times that explores how Hillary Clinton wants to propose more research into medical marijuana and reclassify it as a schedule II kind of drug so that it can be experimented and researched more. This poses a new change towards the public view of the drug as well as opening the door to more research to better understand how it affects the human body. I find it pretty interesting that the drug is used to treat in the relief of cancer patients and other medically related illnesses. If all of these people who use the drug understand that it helps with relief efforts, I wonder how they will feel to know that the drug is also causing them long-term side effects in their hippo-campus. Is it worth the effects? It would surely be up to the person who is using the substance but I can’t imagine the news would be taken lightly. In any case, who is anyone to judge people’s reasoning for the use of the drug? It grows from the earth, it did not magically get synthetically created and it actually provides people with severe pain and illness with some relief. There are several studies out there that provide information that supports the idea that marijuana is not a dangerous substance. In one article by Kim Zimmerman on Live Science website, she explains the health benefits of medical marijuana and how the FDA classifies the drug as a schedule 1 drug which keeps researchers from being able to do detailed studies on it. Once these limitations are removed from the classification of the drug, researchers will be better able to conduct more in depth studies with the substance and be able to better explain how it affects the human body on physiological as well as cognitive levels.

  3. Kayleigh Glynn Beard-maguire

    I want to preface this with the fact that I am a huge supporter of medical marijuana because it has helped many people that I know. There are children that I have seen suffer at the hand of violent seizures and now they use the medical drops and it a different world for them. In fact two of the girls have facebook pages and stories that are out there. One just had bill put into force in Georgia named after her! She lived in Colorado Springs, where I used to live, for a few years until the bill was enacted and now has moved back to GA.

    I have seen my friends suffer from PTSD and now they are better and more lively. They are not always haunted by fears that most don’t fully understand.

    My point is this, there are downsides to everything. Alcohol can affect the hippocampus as well. It can cause issues with LTM and STM. Yet there are more problems with people drinking alcohol than those using marijuana. I am glad that there is research to show what the side effects are, as a patient it is important to know. My concern is that most studies are done to try to show that MMJ is a bad thing when it isn’t. I hear the phrase “no such thing as bad publicity” but that is not true at all.,0

  4. Lia Marie


    As stated in your article, “the THC in marijuana weakens the connections, or synapses, between neurons in the hippocampus.” You also mentioned how these effects are similar, though “not as drastic” as taking the hippocampi out of the brain entirely to stop epileptic seizures, which prompted me to wonder how THC can affect seizures. I remember in the past seeing many sources which tell stories about people who are epileptic taking liquid stains of THC to combat the disease with success and decided to look further into the correlations between THC use, memory functions in the hippocampus and epilepsy. As it turns out, though “marijuana can negatively affect memory,” this side effect is “also a well-known side effect of many antiepileptic drugs” (

    Specifically speaking of using medical marijuana to combat epileptic seizures, studies by Dr. Chu Chen, the Professor of Otorhinolaryngology at Louisiana State University Health Sciences Center has made profound breakthroughs in understanding how THC is induction in the hippocampus ( By discovering the molecular pathway associated with reduced memory function from consuming marijuana, Dr. Chen was then able to find a method to inhibit this side effect of using marijuana. His studies revealed Δ9-THC treatment caused an increase in levels of an enzyme called cyclooxygenase-2 (COX-2), which is seemingly the source of memory problems related to marijuana consumption ( Luckily, they found using OTC nonsteroidal painkillers, like ibuprofen, inhibit COX-2 expression. This cancels out the induction of COX-2 from Δ9-THC, and as a result is “an easy strategy to prevent the side effects of marijuana” ( (

    Sources Cited:

    Chen, Chu. (2014, January 30). Δ9-THC-Caused Synaptic and Memory Impairments Are Mediated through COX-2 Signaling. Cell. Volume 156, Issue 3, Page 618. Retrieved from

    N/A (n.d.). The Use of Medical Marijuana For The Treatment of Epilepsy. Epilepsy Foundation Colorado. Retrieved from

    O’Leary, Mary Beth (2013, November 21). Preventing marijuana-induced memory problems with OTC painkillers. Elsevier. Retrieved from

    Lia Stoffle

Leave a Reply