Analysis of recent study on recreational substance use among patients with premature atherosclerotic cardiovascular disease

You’ve probably seen or heard about this study already.

Main point of concern is the claim that cannabis use reportedly increases the incidence of a heart attack in people with a premature heart condition by 2.5 times. I dug into this a bit, and discovered that like many studies of this nature, the popular press doesn’t understand the difference between absolute and relative effect sizes. 

There are 22 million veterans in the United States, and about 6.6 million of them and their family members received care from the veterans administration in 2014.

We can assume that the numbers have gone up somewhat since then, but they don’t change my calculations here appreciably. Since the number of users of the VA system had increased by about 50% in a 14 year period of time, I added an additional 25% to account for the last seven years. 

About 7700 patients in this observational study presented with a premature heart condition, which appears to have been worsened by cannabis use to the tune of a 2.5 times higher incidence of heart attack. It seems that they were somehow able to isolate people who used cannabis alone from other substances that I would assume to be far more likely to cause a heart attack, such as cocaine and methamphetamine. However, I have not dug deep enough to determine if they actually did this and/or how well they did this.

According to my rough adjustment of the VA patient numbers, 7700 people with premature heart disease out of the estimated 8.2 million who sought care at the veterans administration in 2020 is an incidence of about one case per every thousand patients (.001). If cannabis use increases your odds by 2.5 times, this would mean that there were 2.5 cases per every thousand patients if 100% of the 7700 affected patients were cannabis users. However, I suspect that the number of people who used cannabis while consuming no other more likely culprits such as tobacco, cocaine, and meth, was vanishingly small. I have not yet been able to determine that number from the published study yet. Let’s assume there were only 1000 exclusive cannabis users in this group. That number is probably generously high. That would suggest that the absolute effect size of cannabis use on those with premature heart disease is less than one additional case per 1000 compared to non-cannabis users. 

That is the question that every doctor and patient needs to ask themselves. Is increasing my risk for an adverse effect from 1 out of 1000 to 1.5 out of 1000 a risk that I am willing to take. And that increased risk assumes that there are no other methodological flaws in the study, of which there are many that essentially invalidate it in my opinion. The main invalidating flaw is that there was no attempt to assess comorbidities that may have impacted the patient outcomes.