The Heart Is a Lonely Toker

More tar than the best-selling cigarette.

Posted Feb 28, 2018

We live in interesting times, with many of us the subjects of what is perhaps history’s largest post-marketing study of a “medicine” that never had to be studied pre-market. This medicine has not been approved by regulatory authorities in this country, and yet in many states now it can be obtained with a prescription from a healthcare provider.

How can this be, you ask? Why are we allowing physicians and nurse practitioners and physician assistants to prescribe a medicine without being able to refer to that package insert that lists every side effect even remotely considered related to its use? The right to know, you know?

Well, we are talking marijuana here. 

And the users are the unwitting test subjects who will suffer whatever adverse events there are to be associated with the use of marijuana, informing the rest of us as to what we should watch out for when we next light up.

A recent analysis published in the “Annals of Internal Medicine” tasked itself with elucidating the risks of marijuana to the heart (cardiovascular disease is, after all, the number one cause of death in the world), the researchers focusing on whatever they could to answer that question: Observational studies that were published in English, enrolled adults using any form of marijuana, and reported on vascular risk factors (hyperglycemia, diabetes, dyslipidemia, and obesity) or on outcomes (stroke, heart attack, cardiovascular mortality, and all-cause mortality in cardiovascular cohorts).

It is already known that marijuana smoking, the predominant method of use, causes a five-fold increase in the blood carboxyhemoglobin level and a three-fold increment in the quantity of tar inhaled compared with tobacco. Studies on secondhand marijuana smoke have found dysfunction in the cells lining the vascular system in rats after exposure.

The authors of this article chose to review human data beginning in 1975, as that was the year the Alaska Supreme Court ruled that the “Alaska constitution's right to privacy protects an adult's ability to use and possess a small amount of marijuana in the home for personal use.”  The researchers identified 13 studies examining associations between marijuana use and cardiovascular risk factors, and 11 studies examining associations with clinical outcomes. 

In the 13 studies that looked at vascular risk factors, the evidence examining the effect of marijuana use on diabetes and dyslipidemia was insufficient to permit firm conclusions. For example, while six studies have suggested some metabolic benefits from marijuana use, all were cross-sectional. Most had small sample sizes and included only a one-time assessment of marijuana exposure, or included patients who had only limited exposure to cannabis-related products. The data were just not adequate to make any conclusions.

As mentioned previously, 11 studies examined cardiovascular outcomes, including stroke, heart attack, cardiovascular mortality, and all-cause mortality. The single study that looked at marijuana use as a potential trigger for a heart attack was a case-crossover study that did show an increased risk for heart attack in the first hour after smoking marijuana (not all that surprising, considering that in many individuals marijuana can increase the heart rate and blood pressure).

On the whole, however, evidence examining the effect of marijuana on diabetes, hyperlipidemia, acute myocardial infarction, stroke, and cardiovascular mortality was insufficient, the researchers concluding that studies that follow marijuana smokers over a period of years into the future are needed in order to make the most informed conclusions on the effect of chronic marijuana use on cardiovascular health.

Alas, it takes hundreds of millions of dollars to bring a drug to market in this country. Marijuana is already on the market, without a patent. Who is going to pay for human studies on marijuana? Likely not the drug companies. And likely not the owners of marijuana stores (after all, who wants to hear bad news about a cash crop from which a good livelihood is made)?

So, we remain in limbo. Still, I would suggest, just don’t ask that surgeon to prescribe you marijuana for pain control after your bypass surgery.


Ravi D, Ghasemiesfe M, Korenstein D, Cascino T, Keyhani S. Associations Between Marijuana Use and Cardiovascular Risk Factors and Outcomes: A Systematic Review. Ann Intern Med. 2018;168:187–194. doi: 10.7326/M17-1548