Marijuana, long touted as a safe drug, may put those who use it at risk of suffering a heart attack. A new study found that the risk jumps nearly fivefold during the first hour after smoking marijuana. Dr. Murray Mittleman, the lead author of the study, explains.
Mittleman is also the director of cardiovascular epidemiology at Beth Israel Deaconess Medical Center in Boston, Massachusetts.
What did you find?
This was part of larger study looking at how marijuana impacts our health. We found that a drug many people, middle-aged people, take to relax could trigger a heart attack.
How is it a drug that's known to relax people can cause such stress on the heart?
We know that smoking marijuana raises heart rate. When someone smokes a single marijuana cigarette, there is a dose-dependent increase in heart rate: Typically a doubling in heart rate is not at all surprising. There are also complicated effects on blood pressure. We know from previous studies that when people stand up after smoking marijuana and cigarettes, there can be a dramatic drop in blood pressure and the blood supply to the heart, and this can increase risk of heart attack. We didn't compare the risk of smokers--only looked at people who reported smoking marijuana.
Does paranoia play a role?
It's rare but it could. We know that it increase heart rate and blood pressure. It didn't appear to be factor in the study. But we were looking at experienced users.
The danger did decrease over time. What was the duration of the risk?
The increased risk lasted about 1 hour. In the second hour after smoking the drug, the risk was 1.7 times greater. Starting in the third hour after smoking marijuana, there was no significant risk.
What did you know about the study participants who suffered heart attacks?
Of the 124 patients in the study who reported having smoked marijuana during the year prior to their heart attack, their average age was about 44, and nine people said they had smoked marijuana within an hour before their heart attack. Other studies found a clear ordering in decreased ability to exercise, [to] breathe a supply of oxygen, with marijuana showing the largest effect and the placebo the least.
Who is most at risk?
Middle-aged people with a history of heart disease. People around 40 or 50 years of age with risk factors like high blood pressure. This could be an additional risk they may want to avoid.
How about younger users?
We found that people in their 20s had almost zero risk of increase in heart attack because this group is very unlikely to suffer heart attacks.
What does this study mean to the debate over the medical use of marijuana?
I think it reminds us that it's important to find out if it's safe. It may be a good idea for some people but if you are in a high-risk group, it may not be a good idea. It does highligh the importance of considering potential benefits and risks of taking any substance for medical use.
What's the bottom line?
For young, otherwise-healthy individuals, there's no cause for alarm. But, for older people there may be reason to avoid smoking marijuana.
The study was published in the June 12 issue of the journal Circulation.
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