"In both cases, the blood vessels start to behave less efficiently," UCSF Professor of Medicine Dr. Matthew Springer said.
"In the case of tobacco, this has been known both in humans and rats for quite some time, that tobacco smoke, and second hand smoke included will have this effect, but it wasn't known if marijuana smoke would do the same," Springer said.
Lab rats experienced a severe reduction in their blood vessel function after a minute's exposure to secondhand smoke from either tobacco or marijuana, researchers said.
But, it took the rats three times longer to recover from a minute of secondhand marijuana smoke, compared with tobacco smoke, the researchers found.
"The effect is longer lasting. So, in the case of tobacco, the rats recover in half an hour, and in the case of the marijuana smoke at the same level, one and a half hours after the exposure, it (the rat) still hadn't recovered," Springer said.
The rats' arteries carried blood less efficiently for at least 90 minutes following exposure to marijuana smoke, but began recovering from tobacco smoke within 30 minutes, the study found.
Springer told KCBS that it didn't matter what the marijuana was rolled in, or how it was smoked.
"One of the questions we've received is if the rolling paper had any effect here, because that's burning too – you get smoke from the paper, and any chemicals in the paper. So, what we actually did was we made cigarettes that didn't have paper. We replaced the paper with a stainless steel mesh, and we burned those cigarettes, and the effect was the same," Springer said.
The research was conducted in rats, and has not been tested in humans as of yet.
"Just like you don't want to inhale tobacco smoke, marijuana smoke is not somehow exempt from being smoke," Springer said.
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