The American Heart Association (AHA) has issued a warning to help clinicians and patients become better informed about the potential negative effects of marijuana (cannabis) use on brain health, especially on the young and developing brain, according to a statement published in Stroke.

In many parts of the world, marijuana has become decriminalized or approved for medical use. An estimated 183 million people worldwide used marijuana in 2014 and 22 million fit the criteria for marijuana use disorder in 2016.

Acute marijuana intoxication has been found to impair working and episodic memory, cause impulsivity, and disinhibit certain behaviors. This may be attributed to the location of cannabinoid receptors in areas of the brain involved in executive function and memory.


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Consuming delta-9-tetrahydrocannabinol (THC) interrupts the endocannabinoid signaling pathway, having effects on synaptic plasticity. The short-term consequence of consumption is the disruption of interneural connections, and the long-term consequence is an alteration to the neuronal network. This suggests that exposure to marijuana, especially early in life, may increase risk for structural alterations to functional brain circuitry, particularly in regions associated with cognition and behavior.

The long-term effect on cognition is poorly understood, however, the statement cites recent meta-analyses that found adults who used marijuana at a near daily rate were associated with decreased global neurocognition by about 25% compared with nonusers. The statement also noted in a 25-year longitudinal study, exposure to marijuana decreased verbal memory, while another study found that the frequency of marijuana use at 17 years of age was associated with poorer executive functioning at 23 years of age.

Despite evidence suggesting marijuana use affects cognitive functioning, there has been conflicting data about whether its use affects brain structure and function.

Citing a study of adolescents, it was found that after a five-year follow-up, there was a dose-dependent relationship between marijuana use and prefrontal cortex thinning. However, other studies found no evidence that brain volumes were associated with marijuana use duration or dosage. Overall, studies which used functional magnetic resonance imaging (MRI) approaches found more evidence of the effects of marijuana use in the brain than studies using MRI.

Marijuana use can also impact the sympathetic nervous system, blood pressure, platelet activation, and electrophysiological effects. Marijuana use decreases blood pressure, however, a recent study linked its use with hypertension among individuals aged 30-59 years. Hypertension is an important risk factor for ischemic stroke, hemorrhagic stroke, and subarachnoid hemorrhage. These associations may indicate that marijuana use could have long-term effects on cerebrovascular risk.

Going forward, the statement authors said more longitudinal studies are needed to improve understanding, as observational studies have found conflicting evidence about the effects of marijuana. One source of heterogeneity may be the reliance on self-reported exposure or the co-use of alcohol and tobacco, which may obscure some of the effects of marijuana.

Overall, cumulative evidence suggests that consuming marijuana can have detrimental effects on health, however, the exact mechanism and ramifications have not been precisely established. For this reason, the statement authors concluded “public health efforts should be considered to raise awareness about the potential negative effects associated with the use of marijuana in the general population.”

Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.

Reference

Testai FD, Gorelick PB, Aparicio HJ, et al. Use of Marijuana: Effect on Brain Health: A Scientific Statement From the American Heart Association. Stroke. Published online on February 10, 2022. doi:10.1161/STR.0000000000000396