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Whether marijuana actually causes cardiovascular problems remains unclear, a situation that was not necessarily helped by a study based on 35 reports of cannabis-related complications in France, a country with about 1.2 million recreational users.

I reached out to several cardiologists to gauge their level of concern about the potential risks associated with marijuana, as well as their reactions to the study in particular. Here you'll find their responses, which have been edited as lightly as possible for length and clarity.

, of Baylor Scott and White Health in Temple, Texas

I have a great deal of concern. Previous studies on cardiovascular consequences of smoking marijuana have shown considerable effect on heart rate, as well as swings in blood pressure. Alterations in atherogenic lipoproteins have also been noted in chronic heavy smokers of marijuana. Also, in previous studies, up to a five-fold increase in heart attack was noted in slightly older populations within the first hour after smoking marijuana. As we move further away from medicinal use of marijuana to recreational use, the risk/benefit ratio of the use of marijuana increases.

Limitations: Marijuana use, in the form of smoking, is extremely difficult to study given a lack of strong control groups with extreme variation in THC concentrations and the concomitant use of other drugs (including nicotine in the form of cigarette smoking). The authors are quite up front about this. The other limitations are the lack of understanding as to what the true denominator is and the under-reporting of the potential numerator. There seems to be a more than mere coincidental association between marijuana use in young people and cardiovascular events, although this study certainly cannot fully implicate causation.

I struggle greatly with the issue of legalization of marijuana for recreational use. On one hand, it is a drug with a potential to cause harm. As a physician and a father, I don't want to make it easier for people (especially kids) to get, nor do I want to give the implication of "safety" regarding an agent that still has many questions needing to be answered about its potential negative effects. On the other hand, I do realize that there are recreational drugs (such as alcohol and nicotine) that are presently legalized and regulated which have as much or more potential harm associated with them than does marijuana. The social effects of marijuana being a "black-market" drug in most areas of the the U.S. likely result in many more negative societal outcomes (imprisonment, etc.) and violent injuries/deaths than would legalization of its use with potent regulation, taxation, and the ability to study its effects more closely. Our past attempts at prohibition in this country clearly showed us the severe unintended consequences of the temperance movement with alcohol. Despite obvious rational fears, perhaps it is time to end marijuana prohibition as well?

, Yale University in New Haven, Conn.

This is a highly politicized issue in the U.S. -- whether cannabis is safe and whether people ought to be using it -- and I'm concerned that this article will be overinterpreted. This is data that is highly exploratory. Over about the 4- to 5-year period of this study, there were about 2,000 reports of potential complications associated with marijuana. Among those, there were just a handful that were cardiovascular complications, and I'm actually reluctant to even call them complications. They were events that were observed in people who were using marijuana.

This study is just not positioned to talk about whether or not there was a causal relationship, and truthfully it's not positioned to say whether or not the risk is increasing ... It's not the kind of thing that should hit the front pages. It's not the kind of thing that should really worry people. It's the kind of thing that may make us look into other databases and try to understand this better. The numbers are quite small, it's a voluntary database, and there's no real proof here of the connection. I'm not taking one side or the other, but I am telling you that this particular study should be considered highly exploratory, and we should be very careful about the conclusions that we draw.

, Baylor Heart & Vascular Hospital in Dallas, Texas

The danger of tobacco use as a cause of cardiovascular disease is well known. Chronic marijuana use is known to be dangerous from a neurocognitive standpoint, but there's less data available regarding its use and cardiovascular harm. This study shows that there appears to be an increased risk of cardiovascular events in younger persons who smoke marijuana. This is an important piece of information.

Many patients know about the dangers to their heart and lungs from smoking tobacco, but feel that marijuana smoking is somehow "safer." While there have been , less is known about chronic use and longer-term side effects. This paper gives us some new insights into the potential detrimental effects in a relatively young population.

, National Jewish Health in Denver, Colo.

This is an interesting study that raises the potential for concern, but a lot more rigor is probably needed before we can declare a potential strong association -- or risk or benefit for that matter. There are clearly indicated needs for marijuana treatment, but the harms and the risks are not well characterized. And so I would strongly suggest that additional studies are needed before we can make firm conclusions.

Virtually almost every organ system has cannabinoid receptors or endocannabinoid receptors on them. So the effects are not fully characterized at this point. Essentially it's kind of like putting someone on an unproven drug. You don't know what the effects are going to be necessarily. Weighing the pros and the cons and the uncertainty in this area is the best we can do as clinicians, and then we can just hope that the patient makes their best informed decision.

Am I worried about this? Sort of. I live in Colorado, and Colorado has legal marijuana, and the thing I worry about most is not so much the actual drug necessarily but the way it's taken in. Smoking of any sort is usually more of a risk. And so the thing that I always caution people about is that smoking marijuana usually is using unfiltered means and can very much have some of the effects that smoking and air pollution have already been shown to have in causing or worsening to cardiovascular disease and coronary disease. I think that's a pretty key issue that wasn't touched upon.

, SUNY Downstate Medical Center in Brooklyn, N.Y.

I'm concerned about marijuana use given the expanding use of medicinal marijuana particularly. The reason is that although the data really aren't clear, it appears that there is a link between marijuana use and the likelihood of cardiovascular events. The data are not clear. This is something that has been studied for more than a decade, 2 decades, and it's still not clear that the association is strong. But the effects of the drug are such that it seems plausible that marijuana could cause acute cardiovascular events. The data that have been published most recently suggest, they don't prove, but they suggest that there is a relation between marijuana use and cardiovascular events in the people in the age groups that would be most likely to use marijuana. And that's a real concern. Even if there are relatively few events -- as there were in the study that was published -- the fact that they could happen at all and that they're as devastating as they are leads me to be concerned about increased use.

, University of Colorado Anschutz Medical Campus in Aurora, Colo.

We've got a series of events reported from the years 2006 to 2010, and these are potentially serious: 25% of these events ended in death. And the age range of the subjects in this study was really about 30 to 35. We're talking about young people who don't have much risk for cardiovascular disease ... So what we're seeing is acute myocardial infarction or other forms of acute coronary syndromes that present in patients that have had recent and daily use of marijuana to a large extent.

Now the question that comes up is "What is the prevalence of these cardiovascular disease outcomes?" Keep in mind that we have 35 cases over 4 years, but ultimately less than 5% of cases involving drugs of abuse are reported. So let's say we're only reporting one out of 25 to one out of 30 cases. This could be really a substantial problem. So what do we do about it? I think we need to be aware of the possibility that marijuana-containing products can cause acute cardiovascular disease events, and then, secondly, in the U.S. I think we need to identify a reporting structure where all such events are reported.

, Mount Sinai Heart in New York City

I am concerned about cannabis because we are running a clinic of young people who come to us with coronary artery disease, and I have seen a number of cases in whom I was not able to identify any other risk than the use of cannabis. So I think this registry in France supports the issue. And that is that cannabis is not free of danger for the cardiovascular system. I am not sure if cannabis is more risky than cigarette smoking or less, but one thing is clear: it is affecting young people.

, University of Chicago Medicine

What's most interesting about this data is that it includes mostly younger adults, not older adults for whom we've known there are serious cardiovascular events associated. Also, that it's a rise in that information in the most recent years. And the seriousness of the events was especially striking, in which people were hospitalized or worse. There are some caveats to it: it was 35 events over a number of years among 1.2 million recreational users in France. And it's hard to know if this is a signal or if this is just noise. The bottom line, like any substance we take in our body, there are some benefits and risks associated with them. This highlights the risks potentially associated with recreational marijuana use and makes us all think hard about the relative trade-offs, particularly in medical marijuana use.

CardioBuzz is a blog by Todd Neale for readers with an interest in cardiology.

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