Breathing secondhand marijuana smoke could damage your heart and blood vessels as much as secondhand cigarette smoke, according to preliminary research presented at the American Heart Association's Scientific Sessions 2014.
That leads to the question of how bad second-hand cigarette smoke are known to be. The scientific answer is that there is no evidence - no one has even gotten lung cancer from secondhand smoke. People who seek to make cigarettes illegal say science can't prove secondhand smoke doesn't cause lung cancer, which is then extrapolated to even more speculative concepts like thirdhand smoke. The U.S. Surgeon General's 2014 report on the consequences of smoking claims that secondhand tobacco smoke causes about 34,000 premature deaths from heart disease each year in the United States - but that is because government officials engage in epidemiology and look for a cause to match heart disease to - they find other ways it must be smoking.
The marijuana craze has allowed those smokers to be largely exempt from concerns about the damages of smoking - the political demographic mostly likely to be in favor of bans on cigarette smoking, bans on foods and various other things overwhelmingly favor legalization of marijuana.
But the health risks should not be glossed over to advance a political agenda. In the study, blood vessel function in lab rats dropped 70 percent after 30 minutes of exposure to secondhand marijuana smoke. Even when the marijuana contained no tetrahydrocannabinol (THC) -- a compound in marijuana that produces intoxication -- blood vessel function was still impaired.
Reduced blood vessel function may raise the chances of developing atherosclerosis and could lead to a heart attack. Atherosclerosis is the disease process that causes plaque build-up in the arteries which narrows them and restricts blood flow.
"Most people know secondhand cigarette smoke is bad for you, but many don't realize that secondhand marijuana smoke may also be harmful," said Matthew Springer, Ph.D., senior author of the study and cardiovascular researcher and associate professor of Medicine at the University of California, San Francisco's Cardiology Division.
Marijuana and tobacco smoke are chemically and physically alike
Though the active ingredients in marijuana and tobacco are quite different, the lung damage and risks of heart diseases and various cancers due to smoking are the same. The drop in blood vessel function from THC-free marijuana suggests that the compound isn't responsible for the effect, just as nicotine is not required for cigarette smoke to interfere with blood vessel function.
In the study, researchers used a modified cigarette smoking machine to expose rats to marijuana smoke. A high-resolution ultrasound machine measured how well the main leg artery functioned. Researchers recorded blood vessel dilation before smoke exposure and 10 minutes and 40 minutes after smoke exposure.
They also conducted separate tests with THC-free marijuana and plain air. There was no difference in blood vessel function when the rats were exposed to plain air.
In previous tobacco studies, blood vessel function tended to go back to normal within 30 minutes of exposure. However, in the marijuana study, blood vessel function didn't return to normal when measured 40 minutes after exposure.
Now that marijuana is becoming increasingly legalized in the United States, its effect on others is a growing public health concern, Springer said.
"If you're hanging out in a room where people are smoking a lot of marijuana, you may be harming your blood vessels," he said. "There's no reason to think marijuana smoke is better than tobacco smoke. Avoid them both."
More research is needed to determine if secondhand marijuana smoke has other similar effects to secondhand cigarette smoke in humans.