By Dennis Thompson
"Our review found insufficient evidence to draw meaningful conclusions that marijuana use is associated with cardiovascular risk factors and outcomes," said lead study author Dr. Divya Ravi, an internist with the Wright Center for Graduate Medical Education in Scranton, Pa.
For their review, Ravi and her colleagues pored through medical literature and found 24 studies that evaluated marijuana use and its effects on either heart health risk factors or actual health problems such as heart attack or stroke.
A few studies showed that pot use might benefit the heart, but these were contradicted by other studies that reported potential harmful effects, Ravi said.
For example, some studies linked marijuana use to less diabetes, lower blood sugar and higher levels of "good" HDL cholesterol, the researchers found. And despite anecdotal reports of marijuana bringing on the "munchies," no studies have tied pot use to weight gain or obesity.
"The evidence is insufficient to draw any conclusions," Ravi said. "The association between marijuana and cardiovascular health has not been adequately studied to date."
Two heart experts not involved with the study said they're not surprised by the lack of evidence, given how difficult it is to conduct studies on marijuana use.
Results could become more definitive in the future, thanks to some states legalizing marijuana. That might make people more comfortable discussing their pot use with researchers, said Dr. Russell Luepker, a professor with the University of Minnesota's School of Public Health.
The vast majority of states allow limited use of medical marijuana under certain circumstances. And eight states and Washington D.C. have legalized recreational pot use.
Dr. Satjit Bhusri, a cardiologist at Lenox Hill Hospital in New York City, said it's very likely that smoking pot can harm heart health because you're actively breathing in smoke.
"If you inhale a joint it's like inhaling a cigarette -- you're putting toxins in your body," Bhusri said.
On the other hand, it's hard to say that eating or vaping marijuana produces the same heart risk, said Luepker, a spokesman for the American Heart Association.
"Like any smoked product, you inhale a variety of things, including carbon monoxide and other substances that you certainly don't get if you eat it," Luepker said.
Bhusri also expects that the more someone smokes pot, the more they'd increase their heart health risk.
"I wouldn't be surprised if there is a dose relationship because of these toxins that are inhaled," he said.
But because marijuana users don't smoke at the same rate as those who smoke cigarettes, Luepker said, it's not likely they will be doing themselves as much harm.
For instance, it's hard to think of many people smoking two packs a day of pot, or lighting up first thing in the morning, he said.
Marijuana users are more akin to "social cigarette smokers who smoke a cigarette or two at a party, and they don't seem to have any increased risk from that," Luepker said.
Until more is known, though, pot users should use caution, Ravi concluded.
"At this juncture we have little data on potential harms or benefits associated with use to inform the counseling of marijuana users," Ravi said. "It may be wise to proceed with caution until we have sufficient evidence to comment on the health effects of chronic marijuana use."
The study is published in the Jan. 23 issue of Annals of Internal Medicine.