Marijuana joins smoke-free laws.

• Author: Winterfeld, Amy
• Position: TRENDS & TRANSITIONS

With voters in Colorado and Washington choosing to legalize recreational marijuana, many are looking ahead for any public health concerns that might arise with these new state laws.

Marijuana smoke contains as much tar and 50 percent to 70 percent more carcinogens than tobacco smoke, according to the National Institute on Drug Abuse. And even though marijuana users usually smoke less often, they tend to inhale more deeply and longer than tobacco smokers do, increasing their lungs' exposure to carcinogenic smoke. The institute reports that several studies have suggested marijuana smoke may cause lung cancer, but supporting evidence has been inconclusive.

Other respiratory problems suffered by tobacco smokers, such as chronic coughs, acute chest illnesses and lung infections, may also plague regular marijuana users. Frequent marijuana users, even those who don't smoke tobacco, have more health problems and miss more days of work than nonsmokers, according to the American Lung Association.

To limit exposure to second-hand marijuana smoke, some states have added marijuana to their smoke-free laws. Colorado added medical marijuana when it legalized its use in 2010. Washington's smoke-free law includes "any kind of lighted pipe, cigar...