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DENVER — As more states are legalizing the use of marijuana, some doctors across the country — and in Colorado — are calling for more research to find out if smoking marijuana could possibly cause lung cancer.

Currently, there is no large study showing a direct link between the two.

However, Dr. Jenifer Marks, a general thoracic surgeon at the Medical Center of Aurora, says this is a public health question.

“They are exposing their lungs to foreign materials and foreign irritants that can lead to several known lung conditions. And although we don’t know that lung cancer is one of them, it also took us a really long time to prove that cigarettes and tobacco lead to lung cancer,” Marks said.

But marijuana advocates say this is a question that has been asked and answered.

“Case is closed,” said Mason Tvert, at the Marijuana Policy Project in Denver.

He cites a report from the National Academies of Science, Engineering and Medicine, and studies by UCLA professor Donald Tashkin.

“The longest, largest studies that have been done on cannabis smoking and cancer have concluded that not only is there no link between using cannabis and developing cancer, people who smoke cannabis are less likely to develop these lung problems than people who are non-smokers,” Tvert said.