Using marijuana every day may increase a person’s risk of coronary artery disease, or CAD, by a third compared to those who never participate, a new study finds.
“A growing body of evidence suggests that cannabis is not entirely harmless and may even cause cardiovascular disease,” said Dr. Ishan Paranjpe, the study’s lead author, a family 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.
“So the decision to use cannabis must be carefully weighed against the possibility of serious heart disease,” Paranjpe said.
Coronary artery disease is caused by plaque buildup in the walls of the arteries that supply blood to the heart. CAD, also called atherosclerosis, is the most common type of heart disease, according to the U.S. Centers for Disease Control and Prevention.
Signs of the condition include having angina or chest pain, feeling weak, feel dizzy or nauseous, or short of breath. However, for “some people, the first sign of CAD is a heart attack”, the CDC says on his website.
The study collected data on people enrolled in the All of Us Research Program. The program is administered by the National Institutes of Health and is designed to collect health information from 1 million or more people in the United States.
When enrolling in the study, participants completed a survey about their cannabis use. The research team used that information to divide 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). A few years later, the researchers compared those categories to the participants’ medical records.
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 only used weed once a month or less were not at significant risk, the study found.
The results held up even after researchers ruled out other possible causes of coronary heart disease, such as age, gender and major cardiovascular risk factors — high blood pressure, high cholesterol, type 2 diabetes, obesity, smoking and alcohol consumption.
The study used Mendelian randomization (MR) to determine risk, which other studies on the subject have failed to do, Paranjpe said in an email. The MR method measures gene variations known to be associated with an modifiable risk factor to determine the causal influence of the risk factor.
“While other work has also linked cannabis to CAD, there are several possible confounders that may explain this relationship. Our MR analysis suggests that this relationship may be directly causal,” Paranjpe said.
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 supplies many of the same substances that 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 damage to the heart, lungs and blood vessels, the American Heart Association warned in 2020.
The AHA guidelines then published pointed to studies that found that cardiac arrhythmias, such as tachycardia and atrial fibrillation, could occur within a hours after smoking cannabis containing delta-9-tetrahydrocannabinol or THC. (THC is the part of the marijuana plant that causes a high.)
Other research has shown that smoking cannabis causes heart attacks and leads to a higher risk of strokes and heart failure in people with underlying heart disease.
Remarkable, the new study failed to determine 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, because THC enters the brain faster when smoked, the researchers argue that future research should explore different methods of use and their impact on the heart.