Not all studies are the same. There are good studies. There are bad studies.
Some studies provide preliminary evidence, sort of like clues to a crime. Amy Norton of US News and World Report writes a story titled, “Medical Cannabis for Pain is Linked to Slight Rise in Heart Trouble.” I investigated the finer details of this study noting that it was funded by the National Institute of Drug Abuse with principal investigators admitting to financial relationships with Pfizer, a pharmaceutical company.
Dr. Nina Nouhravesh presented findings from this preliminary study at a European Society of Cardiology meeting in Barcelona, Spain. “In Denmark, there are three approved forms of Cannabis, all taken orally”, says researcher Dr. Nouhravesh. “They include oral solutions and sprays of CBD; teas containing a mix of THC and CBD; and dronabinol, a synthetic form of THC.” Dr. Nouhravesh and other researchers used Denmark’s national database, searching the medical records of 1.6 million patients with chronic pain. Just under 4,600 were medical Cannabis patients who had filled at least one prescription for the three available forms of Cannabis. The study found that those patients who used prescribed Cannabis were 64% more likely to have a heart arrhythmia in six months
Does this sound bad to you? It isn’t. 0.9% or 4,140 patients who used Cannabis had arrhythmias, whereas 0.5% or 800,000 patients who didn’t use Cannabis also had arrhythmias. The relative risk seems significant, but the absolute risk is actually very low. If you don’t pay attention to the math, you can be misled.
It’s known that cannabinoids can influence heart rate, blood pressure, and blood clotting. Add those facts to this study and some people may start to worry. Robert Page, a professor at University of Colorado Skaggs School of Pharmacy sounds concerned as he comments on the study. “Just because something is natural doesn’t mean it’s safe,” he says. Two out of three of the prescribed products in this study are not natural. Why does Professor Page make a comment on natural medicine? I’m not sure. I don’t even know why the quote is in the article.
People with chronic pain often have other health problems and take multiple medications. In this study, 42% of the patients prescribed Cannabis were also taking opiates. Only 12% of patients not taking Cannabis were prescribed opiates. “That’s an important difference,” says Dr. Jim Cheung, chairman of the American College of Cardiology. “Opioid use typically signals severe pain – which itself could trigger arrhythmias.” Dr. Cheung also notes that some arrhythmias are more serious than others, and it’s unclear whether Cannabis is associated with specific types of arrhythmias.
We’ve seen doctors change careers to become politicians. It's also clear that headlines like these are sometimes used as political maneuvers. To uncover truth, scientists discuss or debate facts and repeat studies. As well, scientists usually take a good look at study design and statistics to make conclusions. The answers are not always clear. This story may be a political maneuver or just a misunderstanding of the math by the author. In the end, these authors conclude that more study is warranted. Remember the adage, don’t believe everything you read, especially when it comes to this article about Cannabis in US News and World Report.
Jean Talleyrand, M.D.,