Regular Cannabis Use Linked to Cardiac Abnormalities

Fran Lowry

December 30, 2019

Regular recreational use of cannabis is associated with potentially adverse features of left ventricular size and subclinical impairment of left ventricular function, compared with rare or no cannabis use, an observational study concludes.

Previous use of recreational cannabis was not associated with such features, suggesting that any deleterious effects may not be permanent.

"These are early data which included a relatively small group of regular cannabis users, and the changes we detected were subtle," lead author Mohammed Y. Khanji, MBBCh, PhD, William Harvey Research Institute, NIHR Barts Biomedical Center, Queen Mary University of London, and the Barts Heart Center, St Bartholomew's Hospital, London, United Kingdom, told theheart.org | Medscape Cardiology.

"However, regular users of cannabis may wish to reduce their intake until further systematic research becomes available which will hopefully provide further insight on the long-term effects of recreational cannabis use," Khanji said.

The study was published online December 21 as a letter in JACC: Cardiovascular Imaging.

However, at least one observer is not convinced. Steven E. Nissen, MD, Lewis and Patricia Dickey Chair in Cardiovascular Medicine and professor of medicine, Cleveland Clinic, Ohio, disagrees with the authors' conclusion that healthcare professionals should caution patients on regular use of cannabis.

"This very brief manuscript describes a poorly controlled, observational study suggesting differences in cardiac structure and function in regular cannabis users. The findings are unreliable," Nissen told theheart.org | Medscape Cardiology.

"There were only 47 regular users, and no amount of adjustment can correct for imbalances in the study groups. To conclude that healthcare professionals and policy makers may need to advise caution on regular recreational cannabis use is not warranted based upon these limited data," he said.

However, addiction psychiatrist Thersilla Oberbarnscheidt, MD, University of Pittsburgh School of Medicine, Pennsylvania, warned that cannabis has not been properly studied and that regular use can have serious health side effects.

"It has been shown before that the frequent use of marijuana increased the risk of myocardial infarction and hypoxemia, but a direct pathological effect on the heart has not been shown until now," Oberbarnscheidt told theheart.org | Medscape Cardiology.

"We need more studies to look at the organ toxicity of marijuana," she said. "In the general population, marijuana is seen as natural and 'harmless.' As an addiction psychiatrist, I see many patients who smoke marijuana and are not aware of the toxic effects of that substance," she said.

Khanji said he hopes his study stimulates further research on the cardiovascular health effects of regular cannabis use as well as discussions on the potential public health implications of recreational cannabis.

"Currently, little or no mention of cannabis exists in guidelines on cardiovascular risk assessments or related lifestyle advice guidelines," he noted.

"Our study does have some limitations, including the fact that the study group were mainly Caucasians and we relied on self-reported cannabis usage, which may not be very accurate. The number of regular cannabis users in our study was relatively small. It's also unclear whether the associations observed are due to cannabis use alone or other unmeasured confounding factors," Khanji said.

Discussions of the potential impact of marijuana legalization on public health are hampered by gaps in evidence and variable quality of available data, he added.

Most Widely Produced and Consumed Recreational Drug

A lot has been published about the deleterious effects of smoking cigarettes, but relatively little is known about the effects of recreational cannabis use, the authors say.

"Our team has a clinical and research interest in the prevention of cardiovascular disease. Cannabis is one of the most widely produced and consumed recreational drugs in the world, with over 192 million global users, and so we felt it was important to determine the cardiovascular implication of cannabis use, particularly given the increasing legalization of recreational cannabis," senior author Steffen E. Petersen, MD, PhD, professor of cardiovascular medicine, Barts Health NHS Trust, London, said in an interview.

To study the association between cannabis use and cardiac structure and function, the investigators analyzed cardiovascular MRI data from individuals who did not have cardiovascular disease and who were participants in the UK Biobank population study.

They then categorized self-reported cannabis use into following three categories:

  • "rare/no," meaning no use or less than monthly usage of cannabis;

  • "previous regular," defined as weekly or daily usage of cannabis up to 5 years prior to the interview; or

  • "current regular," defined as weekly or daily cannabis usage within 5 years of the interview.

The study included 3407 individuals. The average age was 62 years, and 55% were women. Of the participants, 47 individuals reported being current regular cannabis users, 105 said they were previous regular users, and 3255 said they were rare or nonusers.

Those who were current regular users were more likely to be younger, male, current tobacco smokers, and to have experienced greater levels of social deprivation compared to rare/never users and previous regular users. They were also less likely to be taking medications for hypertension, Khanji noted.

Regular cannabis use was associated with larger left ventricular size and early signs of impairment of heart function compared to rare/never cannabis users.

Compared with rare/never users, after controlling for age, sex, body mass index, systolic blood pressure, use of cholesterol medication, diabetes, smoking, and alcohol consumption, regular cannabis use was associated with the following:

  • larger indexed left ventricular end-diastolic volume (+5.31 mL/m2; 95% confidence interval [CI], 1.4 – 9.3 mL/m2; P = .008);

  • larger end-systolic volume (+3.3 mL/m2; 95% CI, 0.78 – 5.83 mL/m2; P = .010), and

  • impaired global circumferential strain (–0.78; 95% CI, –1.47 to – 0.09; P = .026).

There were no differences between the groups with respect to left ventricular myocardial mass, ejection fraction, and stroke volume, nor for right ventricular, left atrial, and right atrial parameters.

Interestingly, parameters were similar for previous cannabis users and rare/no users. "This is encouraging and may suggest a dose response or that changes may be reversible after stopping use, as seen in cigarette smoking," Khanji said.

These findings should be interpreted with caution; further research is required to understand the potential pathophysiology and dose-response effects of cannabis use, as well as the long-term implications of regular use on the cardiovascular system, the authors state.

"Health care professionals and policy makers may need to advise caution on regular recreational cannabis use until further systematic research is available," they conclude.

They point out that cannabis use remains illegal in the United Kingdom, "creating additional barriers to reporting usage."

Khanji, Oberbarnscheidt, and Nissen report no relevant financial relationships. Petersen reports a financial relationship with Circle Cardiovascular Imaging, Inc, Calgary, Canada, and Servier.

JACC Cardiovasc Imaging. Published online December 21, 2019. Full text

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