More Research Needed on How Marijuana Affects Human Brain

By Jonathan Springston, Editor, Relias Media

Acknowledging the legal use of marijuana for medicinal and recreational purposes is on the rise, the American Heart Association (AHA) conducted a detailed review of both animal and human studies to learn more about how the drug affects the brain and published this scientific statement.

Marijuana contains two key components: tetrahydrocannabinol (THC), the psychoactive compound that remains illegal federally, and cannabidiol (CBD), which is not psychoactive and has been tested as a treatment for various neurological disorders. The statement authors found studies about how THC affects memory, learning, brain development, social behavior, response to stress, cognition, and more, with gestation and adolescence considered critical periods when marijuana could affect the human brain the most.

The statement authors noted existing literature regarding human studies is more mixed than literature about animal studies. They also nodded to many questions that remain unanswered, such as how various THC levels affect the brain and how people react to marijuana in edible form vs. when they smoke the drug.

"Our understanding of the effects of marijuana on the brain is imperfect, and human research in this area is a work in progress," said Fernando Testai, MD, PhD, FAHA, FAAN, writing group chair and professor of neurology and rehabilitation at the University of Illinois at Chicago. "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."

Indeed, the literature on human subjects research appears mixed depending on the source and angle. For example, there was not an association between marijuana use and a higher risk of early onset ischemic stroke among young patients, as reported in the October 2021 issue of Neurology Alert.

“After adjusting for age, sex, race, and other risk factors, including tobacco smoking, the use of marijuana was not associated with ischemic stroke regardless of the timing of use in relationship to the stroke. There was a trend toward increased stroke risk among those who smoked marijuana at least once a week, but this was not statistically significant,” Matthew Fink, MD, wrote. “In this careful epidemiological study, the analysis does not demonstrate an association between marijuana use and increased risk of early onset ischemic stroke. However, no statement can be made regarding heavy users because of the small numbers of subjects considered to be heavy users at the time of data collection.”

But this report from the February 2022 issue of OB/GYN Clinical Alert mirrors the concerns the AHA scientific statement authors expressed about marijuana use during pregnancy.

“OB/GYNs should work actively to assess the use of marijuana during pregnancy and discuss its harmful effects with patients, including increased aggression, anxiety, and hyperactivity during childhood,” Rebecca B. Perkins, MD, MSc, wrote. “Similar to alcohol, marijuana should be avoided to prevent damage to the developing fetal brain. Patients using marijuana for medicinal purposes should be transitioned to safer medications prior to pregnancy.”

The November 2021 issue of Integrative Medicine Alert includes a broader examination of how patients might be using marijuana from an overall primary care perspective.

For more on this and related subjects, be sure to read the latest issues of Clinical Cardiology Alert.