1 Joint as Damaging as 5 Cigarettes to Your Lungs

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The extensive damage from marijuana results from its higher burn temperature, and because it is inhaled more deeply and held in the lungs longer than cigarettes, Beasley explained. "In addition, there is no filter," he said.

One expert thinks this study is the first to really explain the risks to the lungs posed by marijuana.

"We have always suspected that marijuana causes lung damage, but it's nice to have it quantified," said Dr. Norman Edelman, chief medical officer at the American Lung Association. "Now we can say much more strongly, to people who smoke marijuana, that they are doing bad things to their lungs."

There are still many unanswered questions about marijuana smoking, Edelman said. "Do marijuana smokers go on to get chronic obstructive pulmonary disease?" he asked. "We don't know that."

More information

For more about marijuana, visit the U.S. National Institute on Drug Abuse.