Just about half the country has legalized recreational cannabis, with at least some more states likely to consider it in the near future. But as enjoyable as cannabis can be for many, research out today may highlight a possible drawback of the drug: a higher risk of cardiovascular problems.
Researchers in Boston looked at hospitalization rates in parts of the country that legalized cannabis earlier than others. Compared to the pre-legalization era and to non-adopters, rates of several cardiovascular outcomes—including heart attacks—rose in the western half of the U.S. that first adopted recreational cannabis, they found. Though this study isn’t definitive proof that cannabis can cause heart trouble, it’s the first study to explicitly link the expansion of legal cannabis to such issues, the researchers say.
“Our findings point to potential adverse effects of recreational legalization on population health,” the authors wrote in their study, published today in the journal BMJ Open.
A natural cannabis experiment
Numerous studies and case reports in recent years have tied cannabis use to a higher risk of cardiovascular diseases. Yet other studies have failed to find any link, and some have even suggested that certain ingredients in cannabis like cannabidiol can actually lower blood pressure.
According to the researchers, studying the possible health effects of cannabis through the lens of legalization can offer some advantages over studies that look at individual-level cannabis use. People who use cannabis might differ in other important and not-so-easily visible ways that could affect their risk of certain health problems from people who don’t use it, for instance. The history of recreational legalization in the U.S. also created a sort of a natural experiment that the researchers could study.
In 2014, Colorado became the first U.S. state to legalize pot, following the passage of a ballot initiative in 2012. Over the next several years, many states in the western U.S. quickly followed suit. By 2018, most people in the region either lived in a state or next to a state that sold cannabis legally. However, it wasn’t until late 2018 that Massachusetts became the first eastern state to open legal dispensaries. Given this trend, the researchers could look at what happened to early adoptors post-legalization.
The team analyzed data from the National Inpatient Sample, the largest publicly available database of hospitalized patients collected from medical centers across the country.
They specifically looked at hospital diagnoses related to cardiovascular disease from 2012 to 2018, with a particular focus on the Western census region of the U.S., which includes the states Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, and Wyoming. They compared hospitalization rates in this region before and after legalization started to take hold in 2014; they also compared rates between the western and other regions of the U.S. during this study period.
Before legalization, hospitalization rates in the western U.S. were generally lower than elsewhere in the country, but they began rising more rapidly after 2014. After adjusting for possible factors, the team found a statistically significant link between cannabis legalization in the West and increasing rates of three cardio-related outcomes. For each year of legal cannabis, rates of atrial fibrillation (an irregular heartbeat), heart failure, and heart attacks rose by roughly 2%, nearly 4%, and around 3%, respectively, they calculated.
What should this mean for cannabis and the heart?
This research is still observational, meaning it can only demonstrate a correlation between cannabis legalization and rising hospital visits from cardiovascular disease, not a clear cause-and-effect relationship. The data used in the study also isn’t specific enough to compare individual states to one another.
That said, the researchers did carry out other analyses to strengthen their conclusions. They found that cannabis-related diagnoses also increased in the western U.S. post-legalization, while rates of urinary stones—a condition that likely has no connection to cannabis—stayed stable. This suggests that legalization really did help increase health problems related to cannabis on a population level, some of which may involve our cardiovascular system.
The authors certainly aren’t calling for cannabis to be outlawed. At the same time, they say their findings support “a cautious approach” to future legalization—an approach that would allow for detailed data collection of cardiovascular outcomes in places that adopt recreational weed. They also argue their results support ongoing efforts to reclassify cannabis from a Schedule I controlled substance in the U.S. to a Schedule III drug.
Importantly, a Schedule III classification would make it easier for scientists to study cannabis and its health effects in the lab (in April, the federal government reclassified medical cannabis as Schedule III, though it is still evaluating a decision on recreational cannabis). And this sort of research would help answer relevant questions, such as identifying the exact components of cannabis that might raise people’s heart risk, whether there’s a threshold effect (daily versus occasional use), or if the route of administration matters at all (say, smoking it versus edibles).
Recreational cannabis is here to stay, but we need to learn more about how it can influence our health, good and bad.
