New Study Tells Nothing About Marijuana’s Role in Heart Disease
A new study on marijuana appeared in Journal of the American Heart Association. These are interesting data, but we have to interpret them very carefully.
Sure, we know cannabis can raise heart rate briefly, but most users develop tolerance to the effect. We’ve also seen (in a much larger sample) that it doesn’t increase mortality rates even among survivors of heart attacks.
But the new study made the news anyway. Investigators specifically searched a French database where physicians are legally bound to report any drug-related case that they view as “leading to temporary or permanent functional incapacity or disability, to inpatient hospitalization or prolongation of existing hospitalization, to congenital anomalies, or to an immediate vital risk or death.”
They then looked for cannabis users and found a shade less than 2,000 in the past 5 years. It’s impossible to know what that number means without knowing the number of people these physicians saw or how many patients used cannabis and did not end up reported to this database.
They then found a whopping 35 of these who had cardiac complications. It is impossible to know what to make of this number without knowing the number of cannabis users in France, which the authors report is 1.2 million. If you divide 35 by 1.2 million you get roughly .00003. I’m guessing that not all these cannabis users went to the doctor and not every person who used cannabis and had cardiac complications fessed up to the doctor, so let’s say that we’re off by two orders of magnitude. Let’s give the prohibitionists the benefit of the doubt and multiply by 100. That’d put the rate of problems up to .003.
If those are the chances of having cardiac complications as a French cannabis user, my first thought is that using cannabis protects people from cardiac problems. We need a comparison group of people who don’t use cannabis to know their rate of cardiac problems, but, as the authors point out, we simply don’t have those data. The closest estimates were 57 per 10,000 people, based on another study, which is .0057, or almost twice as bad as the rate among the cannabis users (after our generous overestimation). I’m not going to hold my breath for the the headline, “Cut your heart disease in half with cannabis.”
In short, this study tells us a lot about what kinds of cardiac complications appeared in people who were reported to the French government for cannabis-related problems, but tells us little about the link between cannabis use and cardiovascular disease.
April 24, 2014