Cannabis intake has been shown to cause short-term memory loss in users. This is likely due to the effect that cannabis has on the hippocampus, which is responsible for memory formation. The hippocampus is one of the first areas of the brain to be affected by THC, and this can lead to difficulties in forming new memories and recalling old ones. Long-term cannabis use may also have negative consequences on memory. Heavy cannabis users are more likely to experience problems with verbal memory, learning, and attention span. These effects were most pronounced in people who began using cannabis during adolescence. It is still unclear whether these cognitive deficits are permanent or if they can be reversed with abstinence from cannabis.
According to Blest-Hopley et al. (2020), the hippocampus is involved in cognitive processes such as memory formation and retrieval. It is also thought to play a role in emotional processing. Damage to the hippocampus can lead to problems with memory and learning, as well as changes in mood and behavior. For example, people with damage to their hippocampus may experience episodes of severe depression, anxiety, or paranoia. THC impairs these processes by disrupting the synaptic activity in the hippocampus. This disrupts communication between neurons and results in an inability to form new memories or retrieve old ones. In addition, THC causes changes in brain architecture that further interfere with memory formation and retrieval. These changes cause shrinkage of the hippocampus, which leads to impaired cognition and memory loss (Blest-Hopley et al., 2020). The long-term effects of THC on the brain are not well known, but studies have shown that regular use of marijuana can lead to changes in brain structure and function. These changes can persist even after people stop using marijuana.
The research is similarly supported by Prini et al. (2020), who suggest that neurobiological mechanisms underlying cannabis-related memory loss are only partially understood. However, there seems to be a consensus that cannabinoid exposure causes memory impairment. Animal studies have shown that cannabinoid exposure leads to deficits in spatial memory, working memory, and inhibitory avoidance learning. Human studies have found that cannabinoids impair episodic memory (memory of autobiographical events) and declarative memory (memory of facts). Together, these findings suggest that cannabis exposure can significantly impair cognitive functioning. Blest-Hopley et al. (2020) asserted by giving an example of the impacts of cannabis on education performance. The authors mention that cannabis use can acutely impair memory and thereby impair education attainment. A systematic review of human neuroimaging studies published in 2020 found that cannabis use is associated with reduced neural efficiency and altered brain activation patterns during cognitive task performance.
The authors note that the majority of the reviewed studies found disruptions in activations or reductions in task-related activation clusters among cannabis users. This suggests that cannabis consumption can adversely affect cognitive function, including memory, and lead to an impairment in educational attainment. Nestoros et al. (2017) as well argued that chronic heavy cannabis abuse may result in long-lasting effects on memory. Memory impairment has been found to persist even after abstaining from cannabis use for up to a few weeks. This study also found that heavy cannabis users displayed deficits in immediate and delayed memory recall tasks. On the same, Blest-Hopley et al. (2020) expounded that cannabis exposure during adolescence has been found to be particularly harmful to cognitive development and can affect learning, attention, and mental processing speed. The main psychoactive ingredient in cannabis is THC (delta-9-tetrahydrocannabinol). When THC enters the brain, it attaches to specific receptors called cannabinoid receptors. These receptors are located in areas of the brain that influence pleasure, memory, thinking, concentration, movement, coordination, and sensory perception.
These impairments were still present despite the fact that subjects had no history of psychiatric disorders and did not meet the diagnostic criteria for cannabis abuse or dependence. According to Nestoros et al. (2017), chronic cannabis users had lower scores on memory tests. This was especially true for tests that required participants to remember new information. There are a few possible explanations for this finding. First, cannabis may interfere with the process of forming new memories. Second, cannabis may make it harder to access memories that have been stored in the brain. Third, chronic cannabis use may damage cells in the brain that are important for memory formation and retrieval. Finally, some of the effects of cannabis may last long after people stop using the drug. Blest-Hopley et al. (2020) similarly affirmed that chronic cannabis use might damage cells in the brain.
The authors conducted studies that investigated cannabis use and its effects on the brain. They found that chronic cannabis use was associated with changes in brain structure and function, specifically in the areas of the brain responsible for learning, memory, and attention. Additionally, chronic cannabis use was also associated with poorer performance on cognitive tests and an increased risk of psychiatric disorders such as anxiety and depression (Blest-Hopley et al., 2020). These findings suggest that chronic cannabis use may have negative consequences for brain health, especially in terms of cognition and mental health.
Morgan et al. (2010) similarly confirmed that cannabis users showed increased levels of hyper-priming, which is a phenomenon where people are more likely to identify related items in a list of words. The authors suggest that this increase in hyper-priming is due to the decreased ability of cannabis users to discriminate between stimuli while they are intoxicated. Cannabis has also been shown to impair memory function, especially the ability to recall past events (Morgan et al., 2010). This impairment in memory function is likely due to the disruption of long-term potentiation, which is how memories are formed and stored in the brain.
In accordance with Prini et al. (2020) research, it is well known that cannabinoids exert their psychoactive effects through the activation of cannabinoid receptors located in different brain regions, including the prefrontal cortex and hippocampus. The prefrontal cortex is responsible for executive functions such as planning, organizing, and moderating behavior. The hippocampus is responsible for memory formation and spatial navigation. Damage to either of these areas can lead to cognitive deficits (Prini et al., 2020). Additionally, cannabis use has been linked with increased levels of inflammation in the brain, which can also lead to cognitive decline.
In contrast, Blest-Hopley et al. (2020) proposed a solution to reducing the impacts of cannabis on humans, such as inflammation in the brain. They held that there is growing evidence that abstinence from cannabis use can lead to reduced impacts on the brain. The authors found that abstaining from cannabis produces neurocircuitry changes associated with reduced impulsivity, withdrawal symptoms, and improved cognitive functioning. They concluded that abstinence from cannabis might serve as a protective factor against further neurocognitive decline. Given the growing body of research on the potential harms of cannabis use, it is clear that abstinence is the best way to reduce these risks.
Blest-Hopley, G., Giampietro, V., & Bhattacharyya, S. (2020). A systematic review of human neuroimaging evidence of memory-related functional alterations associated with cannabis use complemented with preclinical and human evidence of memory performance alterations. Brain Sciences, 10(2), 102.
Morgan, C. J., Rothwell, E., Atkinson, H., Mason, O., & Curran, H. V. (2010). Hyper-priming in cannabis users: A naturalistic study of the effects of cannabis on semantic memory function. Psychiatry Research, 176(2-3), 213-218.
Nestoros, J. N., Vakonaki, E., Tzatzarakis, M. N., Alegakis, A., Skondras, M. D., & Tsatsakis, A. M. (2017). Long-lasting effects of chronic heavy cannabis abuse. The American Journal on Addictions, 26(4), 335-342.
Prini, P., Zamberletti, E., Manenti, C., Gabaglio, M., Parolaro, D., & Rubino, T. (2020). Neurobiological mechanisms underlying cannabis-induced memory impairment. European Neuropsychopharmacology, 36, 181-190.