Effects of smoking marijuana every day: Study shows it can raise risk of coronary heart disease
Using marijuana every day can raise a person's risk of coronary artery disease, or CAD, by a third compared with those who never partake, a new study found.
"A growing body of evidence suggests that cannabis is not entirely without harm and may actually cause cardiovascular disease," said lead study author Dr. Ishan Paranjpe, a resident physician at Stanford University.The study - which has not yet been published -- will be presented Sunday at the annual meeting of the American College of Cardiology.
"Thus, the decision to use cannabis must be carefully weighed against the potential for serious heart disease," Paranjpe said.
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Coronary artery disease is caused by plaque buildup in the walls of the arteries that supply blood to the heart. Also called atherosclerosis, CAD is the most common type of heart disease, according to the US Centers for Disease Control and Prevention.
Signs of the condition include having angina, or chest pain, feeling weak, dizzy or sick to your stomach, or experiencing shortness of breath. However, for "some people, the first sign of CAD is a heart attack," the CDC says on its website.
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Using once a month or less
The study pulled data on people participating in the All of Us Research Program. Administered by the National Institutes of Health, the program is designed to gather health information over time from 1 million or more people in the United States.
When enrolling in the study, participants completed a survey on their cannabis use. The research team used that information to place those who responded into five categories: Daily users (4,736 people), weekly users (2,720), monthly users (2,075), those who used once or twice in three months (8,749) and those who never used (39,678 people). The researchers then compared those categories with participants' medical records a few years later.
They found that daily cannabis users were 34% more likely to be diagnosed with coronary artery disease than those who had never used the drug.
People who used weed only once a month or less had no significant risk, the study found.
The results held true even after researchers factored out other potential causes of coronary heart disease, such as age, sex and major cardiovascular risk factors - high blood pressure, high cholesterol, type 2 diabetes, obesity, smoking and alcohol use.
The study used Mendelian randomization (MR) to determine risk, which other studies on the topic have not, Paranjpe said in an email. The MR method measures gene variations known to be related to a modifiable risk factor to determine the causal influence of the risk factor.
"While other work has also linked cannabis with CAD, there are several potential confounders that may explain this relationship. Our MR analysis suggests this relationship may be directly causal," Paranjpe said.
Marijuana and the heart
Why does marijuana appear to damage the heart and blood vessels? First, it increases heart rate and blood pressure immediately after each use, according to the CDC.
"Marijuana smoke also delivers many of the same substances researchers have found in tobacco smoke - these substances are harmful to the lungs and cardiovascular system," the agency says.
Smoking or vaping any substance, including cannabis, should be avoided due to the risk of harm to the heart, lungs and blood vessels, the American Heart Association warned in 2020.
The AHA's guidance released then pointed to studies that found heart rhythm abnormalities, such as tachycardia and atrial fibrillation, could occur within an hour after weed containing delta-9-tetrahydrocannabinol, or THC, was smoked. THC is the part of the marijuana plant that creates a high.
Other research has shown smoking weed has triggered heart attacks and leads to a higher risk of strokes and heart failure in people with underlying heart disease.
Notably, the new study was not able to tease out whether different types of cannabis use - such as consuming edibles versus smoking weed, for example - made a difference in a person's risk of developing CAD. However, since THC gets to the brain faster when smoked, the researchers argue future research should investigate various usage methods and their impact on the heart.
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