Mitch Earlywine is Associate Professor of Psychology at the State University of New York at Albany and author of "Understanding Marijuana: A New Look at the Scientific Evidence." You can chat with him about this article at our Discussion Board.

Although links between cannabis (marijuana) use and lung cancer have now been called into question, regular cannabis smoking still leads to respiratory problems like coughing, wheezing, hacking up phlegm, and shortness of breath. The human lung has evolved to breathe clean air, so inhaling any sort of smoke, especially day after day, is truly irritating. 

These respiratory effects of smoking continue to be part of the argument against medical cannabis, too. I can't imagine anybody suffering from AIDS-related wasting or the nausea associated with chemotherapy could possible care about a little cough. Nevertheless, opponents of medical cannabis continue to emphasize that a smoked medicine must be a bad idea. 

I'm happy to say that recent work on the vaporizer should put this argument to rest. Vaporizers heat cannabis to about 180degrees Centigrade (about 350 degrees Fahrenheit). The plant releases its THC without ever catching fire, so the toxins associated with burning don't appear. 

Two new studies reveal that cannabis vapor is unlikely to create any respiratory symptoms. The new work stands on the shoulders of a classic experiment performed over a decade ago by Dr. Dale Gieringer. Dr. Gieringer's data suggested that the vaporizers of the day had a lot of potential for administering THC without the tars associated with burning. This work also revealed that the water pipe, a favorite of many users, did not have the ideal ratio of THC to tars that people would hope. A subsequent study showed that the latest vaporizers deliver THC in a fine mist without a trace of any harmful tars or carcinogens.

But research with live people who used the vaporizer was still rare. Work from 2007 shows that the new vaporizers can genuinely deliver on their promise. Dr. Donald Abrams and his crew at the University of California, San Francisco, had 18 people use the vaporizer or smoke a joint. They found that joints increased carbon monoxide in the lungs. (Carbon monoxide is the deadly gas that comes from the tailpipe of a car or a lit cigarette.) In contrast, the cannabis vapor did not increase carbon monoxide in the lungs, suggesting that the vaporizer is less likely to lead to lung problems.

A paper of mine also addresses this issue. My paper showed that folks who use a vaporizer are less likely to report respiratory symptoms like coughing, wheezing, shortness of breath, and tightness in the chest. As you might guess, folks who smoked cigarettes were much more likely to report these symptoms. The more cannabis that people used, the more the vaporizer seemed to help. 

Although calls for more work will undoubtedly continue, the switch to the vaporizer looks like the perfect step for cannabis users who have any respiratory symptoms.

The author is available to chat about this article at our  Discussion Board.