Risks from secondhand marijuana smoke?

SAN FRANCISCO» The inspiration arrived in a haze at a Paul McCartney concert a few years ago in San Francisco.

“People in front of me started lighting up, and then other people started lighting up,” said Matthew Springer, a biologist and professor in the division of cardiology at the University of California-San Francisco. “And for a few naive split seconds I was thinking to myself, ‘Hey, they can’t smoke in AT&T Park! I’m sure that’s not allowed.’ And then I realized that it was all marijuana.”

As the visible cloud of pot smoke took shape, so did Springer’s idea to study the effects of secondhand marijuana smoke: Do people just assume cannabis smoke isn’t harmful the way tobacco smoke is?

Springer already was researching the health effects of secondhand tobacco smoke on rats at his lab. He decided to run the same tests using joints.

In the lab, Springer puts a cigarette or a joint in a plastic glass box. Then he lights it and lets the chamber fill with smoke, where an anesthetized rat is exposed to the smoke.

So far, Springer and his colleagues have published research demonstrating that secondhand tobacco smoke makes it harder for the rats’ arteries to expand and allow a healthy flow of blood.

With tobacco products, this effect lasts about 30 minutes, and then the arteries recover their normal function. But if it happens over and over, the arterial walls can become permanently damaged, and that damage can cause blood clots, heart attack or stroke.

Springer demonstrated that, at least in rats, the same physiological effect occurs after inhaling secondhand smoke from marijuana.

And, the arteries take 90 minutes to recover, compared with the 30 minutes with cigarette smoke.

Springer’s discovery about the effect on blood vessels describes just one harmful impact for nonsmokers who are exposed to marijuana. Statewide sampling surveys of cannabis products sold in marijuana dispensaries have shown that the items may contain dangerous bacteria or mold, or residue from pesticides and solvents.

But even if the cannabis tests clean, Springer said, smoke itself is bad for the lungs, heart and blood vessels.

Other researchers are exploring the possible relationship between marijuana smoke and long-term cancer risk.

Certainly, living with a smoker is worse for your health than just going to a smoky concert hall. But, Springer said, the less you inhale any kind of smoke, the better.