Researchers found exposure to secondhand marijuana smoke for just 1 minute impaired rats' blood vessel function.
What is more, researchers found that it may take three times as long for blood vessel function to recover after inhalation of secondhand marijuana smoke, compared with inhalation of secondhand tobacco smoke.
Senior author Matthew Springer, Ph.D., professor of medicine in the Division of Cardiology at the University of California-San Francisco, and colleagues report their findings in the Journal of the American Heart Association.
The harms of exposure to secondhand tobacco smoke are well established, and these include immediate damage to the heart and blood vessels.
But according to the research team, little is known about the harms that may arise as a result of exposure to secondhand marijuana smoke.
To find out, Springer and colleagues exposed rats to either secondhand tobacco or marijuana smoke for 1 minute.
The team assessed the blood vessel function of the rodents before and after exposure to each form of smoke. Specifically, they looked at how the smoke impacted the blood vessels' ability to transport blood, and if impairment occurred, how long it lasted.
Lengthy blood vessel recovery with secondhand marijuana smoke
The researchers found that exposure to both types of smoke impaired the rats' blood vessel function, but secondhand marijuana smoke appeared to have a more damaging effect than secondhand tobacco smoke.
Following exposure to secondhand tobacco smoke, it took 30 minutes for the rodents' blood vessel function to recover, but it took at least 90 minutes for their blood vessel function to recover after exposure to secondhand marijuana smoke.
Additionally, the team found that it was not the chemicals in marijuana - such as tetrahydrocannabinol (THC) - that were responsible for blood vessel impairment, but rather burning of the plant material itself.
Such blood vessel damage - despite its temporary nature - could have long-term health implications.
"While the effect is temporary for both cigarette and marijuana smoke, these temporary problems can turn into long-term problems if exposures occur often enough and may increase the chances of developing hardened and clogged arteries."
Matthew Springer, Ph.D.
While the study was conducted in rats, the researchers note it is highly likely that secondhand marijuana smoke has the same effect on human blood vessel function.
"Arteries of rats and humans are similar in how they respond to secondhand tobacco smoke, so the response of rat arteries to secondhand marijuana smoke is likely to reflect how human arteries might respond," says Springer.
Marijuana is the most commonly used illicit drug in America, though the drug has been legalized in a number of states for recreational or medicinal purposes, meaning an increasing number of people are likely to be exposed to secondhand marijuana smoke.
As such, Springer and colleagues note it is important to gain a better understanding of the possible health implications of such exposure, and further research in this field is warranted.
In the meantime, the team advises avoiding all forms of smoke, whether from tobacco or marijuana.