Pot Impacts Heart, Study Shows

From the WebMD Archives

March 2, 2000 (San Diego) -- The Woodstock generation is getting some very bad news: Marijuana smoking in middle age may trigger a heart attack in those who still indulge. Marijuana smokers increase their risk of having a heart attack almost five times within one hour of lighting up, according to a study presented here at an American Heart Association (AHA) meeting.

"This is the first documented link between marijuana and heart attack," says Murray A. Mittleman, MD, PhD, of Beth Israel Deaconess Hospital in Boston.

Mittleman tells WebMD the spike in risk quickly decreases after an hour passes. Pot smokers are twice as likely as nonsmokers to have a heart attack one to two hours after lighting up.

To put that increased risk in perspective, Mittleman says that the risk of heart attack increases 100 times when a couch potato decides to shovel snow, and it "increase[s] 2.5-fold with sex."

AHA president Lynn A. Smaha, MD, PhD, tells WebMD that he will share the findings with colleagues, such as cancer specialists, who may be prescribing medical marijuana to treat nausea and poor appetite. "Any drug has the potential for adverse side effects," says Smaha. He says marijuana should be approached with the same caution as that used with other drugs.

A third of the patients studied by Mittleman and colleagues were women, and the age range was 20 to 92. The patients were interviewed three days after having a heart attack. The interviews were designed to determine any possible contributing factor during the days and weeks leading up to the heart attack, according to Mittleman.

Of the nearly 3,900 people Mittleman studied, about 3% reported being regular marijuana users. Thirty-seven said they smoked marijuana within 24 hours of the heart attack, and "nine patients said they used it within an hour of [the onset of symptoms]," says Mittleman.

Smaha says it is clear that "more research needs to be done to delve into the mechanism at work here." Mittleman agrees and says that his study doesn't provide enough information to determine whether it is marijuana itself that is causing the increased risk or whether it is associated with other elements in the smoke, such as carbon monoxide. He says it is clear that "inhaled fine particles have adverse health effects." But the risk appears to be limited to older marijuana smokers. "Most of the regular marijuana users in the study were in their 40s and 50s and the oldest was 68."

Mittleman did note some interesting differences between the users and nonusers of marijuana. Those who had smoked marijuana prior to having a heart attack were much younger, with an average age of 44 compared to 62 in the nonsmokers. Also, the marijuana users were less likely to have other risk factors for heart disease, such as high blood pressure and diabetes, and were less likely to have had a history of chest pain prior to the heart attack, says Mittleman.

The study also shows that frequent marijuana use was certainly not a requirement to be at risk of having a heart attack. Of the marijuana users, 32 used it a few times a month and 40 used marijuana less than once a month, Mittleman says.

The Marijuana Policy Project (MPP), a Washington-based group that lobbies for laws to decriminalize marijuana use and supports the use of medical marijuana, immediately issued a press release warning that the study could be misinterpreted. MPP spokesperson Chuck Thomas tells WebMD, "Our concern is that some legislator is going to say that marijuana causes heart attacks. That's not what this study says." Six states have decriminalized marijuana use and several others are considering similar laws. Thomas says the risk of adverse events with marijuana use is "comparable to [the] risk associated with legal drugs."

At a press conference, several reporters asked about the timing of the study. Mittleman says that his team decided to do the study in response to last year's report on marijuana from the Institute of Medicine (IOM). That report concluded that there was no significant risk of heart disease due to marijuana in young marijuana users but urged a study of its effect in older populations. "We just decided to take IOM up on that suggestion."

Vital Information:

  • New research reports that during the first hour after smoking marijuana, one's risk of heart attack jumps nearly five times. By comparison, a sedentary person shoveling snow increases heart attack risk 100 times. Having sexual intercourse would raise heart attack risk in the same person 2.5 times.
  • Observers say the apparent risk of heart attack should be considered even in cases where the drug is used medically, such as in cancer patients. Marijuana legalization advocates say they fear legislators will interpret this study as a warning that marijuana causes heart attacks.
  • Experts add that researchers still need to figure out what marijuana does to the body and why those changes may increase heart attack risk. Scientists also do not know if the drug itself triggers heart problems or if a component in the smoke is to blame, such as carbon monoxide