Cannabis & Brain: Where are we Today?
News release, Polyphenols Applications - 17 March 2022, Valencia - Spain
Despite the perception that marijuana is harmless, there is some scientific evidence challenging that belief, and there are many unanswered questions about its impact on brain health, according to a new American Heart Association scientific statement published today in the Association's journal Stroke.
The most studied chemicals in cannabis are THC and CBD. THC is the compound in marijuana that gives the sensation of being high. CBD (cannabidiol) has antioxidant and anti-inflammatory properties but does not have psychoactive effects. The potential therapeutic benefits of CBD continue to be investigated in clinical trials.
To fully understand the potential impact of marijuana, it's important to know that the human body naturally produces compounds called endocannabinoids that are similar to those in marijuana.
Endocannabinoids, as well as THC, can attach to neurons in the brain through molecules called cannabinoid receptors. When THC activates cannabinoid receptors in the brain, it can disrupt the normal actions of endocannabinoids. "These receptors are highly concentrated in brain areas related to cognition," said Testai.
According to the statement, previous animal studies (in rodents) indicate that prolonged exposure to THC disrupts memory and learning, and impacts brain development and maturation in specific ways if exposed at certain stages of life.
"Data obtained in these animal studies demonstrate that disruption of endocannabinoid pathways leads to behavioral and cognitive abnormalities, such as poorer memory and learning ability and a heightened sensitivity to stress. Also, there may be vital life periods—gestation and adolescence—when the brain may be particularly vulnerable to the impact of THC," Testai said.
While the exact timing and amount of marijuana exposure are more easily controlled in animal studies, as well as controlling the animals' social and environmental conditions, human research studies cannot replicate similar strict parameters. Thus, results from existing studies in humans have been mixed, yet raise similar concerns about the impact of marijuana exposure on brain health. Among the studies in humans summarized in the scientific statement, the findings included:
- While actively using marijuana, people demonstrated worse scores on driving road tests when using THC-dominant marijuana, compared to when they were using CBD-dominant marijuana or no marijuana.
- In young adults who were followed for 25 years as part of a heart disease research project, scores on verbal memory tests declined in correlation to more years of self-reported exposure to marijuana.
- There were more psychological problems and poorer cognitive function in children (average age 9) whose mothers reported using marijuana during pregnancy.
- Marijuana use during adolescence has been associated with thinning in an area of the brain involved in cognition (the prefrontal cortex), with greater exposure to marijuana associated with more thinning. However, other studies detected no difference.
- Structural changes in the brain were visible in some studies comparing marijuana users and non-users. Specifically, there was thinning of brain areas important in orchestrating thoughts and actions, or decreased volume in an area of the brain important for memory. Other studies that compared cognitive testing and brain imaging found no differences between marijuana users and non-users.
- Cannabis users were found to have an increased risk of clot-caused stroke, with one study finding 17% more and another finding 24% more strokes among cannabis users.
The statement also highlights numerous open questions on the impact of cannabis on brain health, including:
- Does marijuana's impact on brain health differ depending on the person's age?
- How does marijuana interact with other substances such as prescription medications? This is a particular concern in elderly people who may be using multiple medications such as blood thinners, antiarrhythmia or anticonvulsant medications to treat other chronic health conditions.
- Do the effects of marijuana differ whether it is used recreationally or prescribed for the treatment of a specific medical condition?
- How much marijuana is too much? In older research studies conducted when marijuana was illegal in all U.S. states, there may have been significant under-reporting of how frequently marijuana was used.
- Do different types of marijuana (such as higher THC levels or synthetic cannabinoids) impact the brain differently?
- Are there differences in brain health depending on whether marijuana is smoked or consumed in an edible product?
"Our understanding of the effects of marijuana on the brain is imperfect, and human research in this area is a work in progress. Still, the results of recent animal studies challenge the widely accepted idea that cannabinoids are harmless and call for caution when using marijuana, particularly while pregnant or during adolescence," said Testai.
Don't forget to join us in Polyphenols Applications 2022, this September, where a Cannabis workshop will be held on the first day. Professional speakers like Dr. Pam Maher will be presenting their most recent finding in this field.
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