Marijuana’s Impact on Cardiovascular Risk Uncertain
By Marilynn Larkin
NEW YORK—A systematic literature review found insufficient evidence to determine whether marijuana has any effect, positive or negative, on cardiovascular risk factors and outcomes, researchers say.
“The few studies that suggested a possible benefit were cross-sectional, and were contradicted by more robust longitudinal studies that reported potential harmful effects,” Dr. Divya Ravi of the Wright Center for Graduate Medical Education in Scranton, Pennsylvania, and Dr. Salomeh Keyhani of the University of California, San Francisco, told Reuters Health.
“With the recent change in policies, clinicians are more likely to encounter the effects of marijuana use, especially among middle-aged patient populations with existing comorbidities,” they said in a joint email. “At this juncture, we have little data on potential harms associated with use to inform the counseling of patients.”
The researchers analyzed data from English-language observational studies, of adults using any form of marijuana, that reported on vascular risk factors such as hyperglycemia, diabetes, dyslipidemia and obesity - or on cardiovascular outcomes and all-cause mortality. All had been published from January 1975 through September 2017.
As reported online January 22 in Annals of Internal Medicine, 13 studies examined associations between marijuana use and cardiovascular risk factors and 11 looked at clinical outcomes.
Six cross-sectional studies suggested a metabolic benefit from marijuana use, but the findings were not supported by prospective studies. Evidence was insufficient to detect an effect of marijuana on diabetes, dyslipidemia, acute myocardial infarction, stroke, or cardiovascular and all-cause mortality, according to the authors.
More recent long-term, prospective studies were limited by recall bias, inadequate exposure assessment, minimal marijuana exposure, and the use of mostly low-risk cohorts.
Drs. Ravi and Keyhani conclude, “There is a need to perform robust longitudinal studies that adequately characterize marijuana exposure, especially among an aging population.”
Dr. John Higgins, a sports cardiologist with McGovern Medical School at UTHealth in Houston, told Reuters Health, “The active ingredients of marijuana, cannabinoids, stimulate cannabinoid receptors CB1 and CB2, which are widely distributed in the cardiovascular system.”
“These receptors, when activated, can modulate the function of various cellular elements of the vessel wall, the immune system, and heart rate/blood pressure - and may contribute to the pathogenesis of atherosclerosis,” he said by email.
“In the short term,” he noted, “we know that marijuana does affect the senses and mood, impairs mental and physical functioning, and can result in psychiatric symptoms such as hallucinations, paranoia and delusions.”
“In addition,” he said, “high-risk behaviors have been associated with people under the influence of marijuana, which can have short- and long-term consequences to their health.”
“The associations of marijuana use with other drugs and dependencies/addictions (also) need to be clarified in order to learn the true effects of marijuana on the body systems,” he concluded.
Two cardiologists from Colorado, where recreational and medical marijuana use are legal, also commented by email. Dr. Larry Allen of UCHealth University of Colorado Hospital, Anschutz Medical Campus in Aurora, said the findings “are consistent with my reading of the literature and with my own experience in taking care of patients.”
“Those who use marijuana are not necessarily the same as those who do not, and thus observational comparisons and associations are highly problematic,” he stressed. “There are plenty of unfounded claims out there for both risk and benefit.”
Dr. Robert Page, Lead Cardiac Transplant Pharmacist at the University of Colorado, said, “Marijuana is not regulated, even in dispensaries, so home-grown products can contain pesticides and fungicides that could contribute to potential cardiovascular conditions.”
“It is just like herbal products,” he continued. The U.S. FDA should do what was proposed due to the association of drinking energy drinks and cardiovascular events. Products were moved to the ‘food’ category for appropriate regulation under the Food, Drug, and Cosmetic Act.”
“However,” Dr. Page acknowledged, “this would warrant changing legislation, and moving marijuana from a schedule 1 drug so we can study the product.”
“We are back in the same situation that we were in the 1950s and ‘60s with cigarette smoking,” he concluded. “Policy makers need to consider well-designed cohort studies now if this question (about cardiovascular risk) is to be answered in the near future.”
Dr. Robert Kloner, Director of the Cardiovascular Research Institute at Huntington Medical Research Institutes in Pasadena, California, said in an email to Reuters Health, “Marijuana use is likely here to stay, and legalized increased use will continue. Just like alcohol, there may be both benefits and deleterious effects of the drug on the cardiovascular system.”
“We need to determine what factors may lead to benefits and what factors may lead to deleterious effects so that we can better educate subjects and patients who use marijuana,” he stressed. “I hope there is increased funding from states and the federal government to better understand the effect of marijuana on the cardiovascular system as well as other organ systems in the body.”
Ann Intern Med 2018.
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