Friday Favorites: Does Marijuana Cause Strokes and Heart Attacks?

Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.

Does the so-called “dark side of cannabis” include stroke––here said to be associated with non-synthetic marijuana––by which I assume they mean, uh: marijuana?

There have been case reports of artery damage due to the vasoconstrictor effect of cannabis, something that’s been well documented. 

One study found cannabis users had 100 times greater odds of suffering from something called multifocal intracranial stenosis, where the arteries inside your brain clamp down at multiple points, but that’s a rare condition. What about strokes?

“The [lack] of high-level evidence regarding the adverse effects of marijuana usage on [brain artery] health has [led to this] notion that recreational marijuana [may not be a problem].” So, they decided to put it to the test. You want high-level evidence, they said. Well, how about a study of literally millions of pot smokers? Okay, then. And they found that recreational marijuana use did seem to be associated with an increased risk of being hospitalized with an acute ischemic stroke––but this may just be among those who smoke regularly, at least once a week.

The reason we think it’s cause-and-effect is that “the majority of [recorded strokes were] during or shortly after marijuana exposure.” And there are even cases in which strokes recurred after marijuana re-exposure. So put all that together, and it makes a convincing case––though you’d really have to like randomize people to smoke pot or placebo pot to be sure. It’s like the heart disease story.

A similar “temporal” relationship has been found between marijuana use and the development of heart attacks and sudden cardiac death––meaning the heart attacks seemed to happen while they were using or right afterwards. However, this is complicated by the fact that cannabis is often used in combination with other drugs, such as alcohol or cocaine. So, you can’t just ask heart attack victims if they were smoking pot at the time, and make the connection without asking about other substance use. Within an hour of snorting cocaine, for example, the risk of having a heart attack goes up more than 20-fold.

That’s about five times more than after smoking pot. The hour after you smoke marijuana, your heart attack risk does appear to nearly quintuple, but only for that hour; then your risk drops down to normal. Okay, but what does that mean? Even though heart disease is our #1 killer, the risk of having a heart attack every hour is only like one in a million in any particular hour. So, even if you then light up a joint, that may quintuple your risk, but that would only bump it to like 1 in 150,000 risk in that hour. But it’s just for that one hour. So, even if you smoked every day, your annual risk might just go up a few percent. But why the increased risk at all?

Well, we’ve known since the 70s that within an hour of smoking a joint, pulse rate goes up about 35 percent. Smoking a single joint increases blood pressure too, as well as carbon monoxide levels in the blood of angina patients, and cuts their ability to exercise nearly in half. Now is that just because of breathing smoke––any kind of smoke? No, smoking a placebo joint, a joint with marijuana from which the THC has been removed, only cuts down exercise capacity like 9 percent, compared to cutting the time they could exercise before the chest pain started by 48 percent with the cannabis. So, it does seem to be a specific drug effect. Now, whether that’s as bad as tobacco we’d never know…until a year later.

Smoking a marijuana cigarette decreased the exercise time until angina more than smoking a tobacco cigarette, which only cut exercise capacity 23 percent, compared to 50 percent after the joint. This may be because marijuana puts more demand on the heart. So, no surprise then that it was worse than tobacco.

It may also be the carbon monoxide. Smoking marijuana leads to nearly five times more carbon monoxide in your bloodstream than smoking tobacco. This is because pot smokers inhale deeper and then hold the smoke in, allowing more carbon monoxide into your system. So, between that and the “cardioacceleration” (the increased heart rate and pressure), that could account for the accelerated chest pain in heart disease patients.

Does it have any chronic effects on the arteries? Cannabis users do seem to have relatively stiffer arteries for their age, suggesting an acceleration of the aging process. And we are only as old as our arteries.

Even second-hand marijuana smoke may be harmful, according to this recent study in the Journal of the American Heart Association entitled “One minute of marijuana secondhand smoke impairs vascular endothelial function,” meaning artery function; and so, there was a call to protect vulnerable populations, including the elderly and disabled, and residents of multi-unit housing, pregnant women, and children. Even just one minute of exposure to marijuana second-hand smoke in rats; so, it’s not clear how applicable this is, outside of perhaps not smoking around your pets.

Please consider volunteering to help out on the site.

• Rose DZ. What a downer: The dark side of cannabis. J Neurol Sci. 2016;364:189-90.
• Lou JY, Randhawa MS, Hornacek D, Bajzer C. Images in vascular medicine. Spontaneous renal artery dissection in a cannabis user. Vasc Med. 2015;20(4):379-80.
• Wolff V, Lauer V, Rouyer O, et al. Cannabis use, ischemic stroke, and multifocal intracranial vasoconstriction: a prospective study in 48 consecutive young patients. Stroke. 2011;42(6):1778-80.
• Rumalla K, Reddy AY, Mittal MK. Recreational marijuana use and acute ischemic stroke: A population-based analysis of hospitalized patients in the United States. J Neurol Sci. 2016;364:191-6.
• Hemachandra D, McKetin R, Cherbuin N, Anstey KJ. Heavy cannabis users at elevated risk of stroke: evidence from a general population survey. Aust N Z J Public Health. 2016;40(3):226-30.
• Hom L, Gannon R. Non-psychological consequences of chronic marijuana inhalation. Conn Med. 2015;79(7):423-8
• Thomas G, Kloner RA, Rezkalla S. Adverse cardiovascular, cerebrovascular, and peripheral vascular effects of marijuana inhalation: what cardiologists need to know. Am J Cardiol. 2014;113(1):187-90.
• Mittleman MA, Mintzer D, Maclure M, Tofler GH, Sherwood JB, Muller JE. Triggering of myocardial infarction by cocaine. Circulation. 1999;99(21):2737-41.
• Mittleman MA, Lewis RA, Maclure M, Sherwood JB, Muller JE. Triggering myocardial infarction by marijuana. Circulation. 2001;103(23):2805-9.
• Beaconsfield P, Ginsburg J, Rainsbury R. Marihuana smoking. Cardiovascular effects in man and possible mechanisms. N Engl J Med. 1972;287(5):209-12.
• Aronow WS, Cassidy J. Effect of marihuana and placebo-marihuana smoking on angina pectoris. N Engl J Med. 1974;291(2):65-7.
• Aronow WS, Cassidy J. Effect of smoking marihuana and of a high-nicotine cigarette on angina pectoris. Clin Pharmacol Ther. 1975;17(5):549-54.
• Wu TC, Tashkin DP, Djahed B, Rose JE. Pulmonary hazards of smoking marijuana as compared with tobacco. N Engl J Med. 1988;318(6):347-51.
• Reece AS, Norman A, Hulse GK. Cannabis exposure as an interactive cardiovascular risk factor and accelerant of organismal ageing: a longitudinal study. BMJ Open. 2016;6:e011891.
• Wilson KM. Secondhand marijuana smoke is not benign. J Am Heart Assoc. 2016;5(8).
• Wang X, Derakhshandeh R, Liu J, et al. One minute of marijuana secondhand smoke exposure substantially impairs vascular endothelial function. J Am Heart Assoc. 2016;5(8).

Video production by Glass Entertainment

Motion graphics by Avocado Video

Image from DavidCardinez via Pixabay