Smoking marijuana may cause precancerous changes in the lungs, Reuters Health reported on July 13.

A review of 19 studies, performed by a team at Case Western Reserve University in Cleveland, Ohio, found a link between marijuana use and certain changes in lung tissue that promote cancer, including oxidative stress, dysfunction of tumor-fighting cells, changes in tissue structure and DNA alterations.

People who smoked marijuana had more of these cancer-promoting changes in their lung tissue than did non-smokers or those who smoked cigarettes, the researchers state in the Archives of Internal Medicine.

However, current findings do not prove that marijuana smoking causes lung cancer.

Doctors should warn their patients that smoking marijuana does have potential adverse affects, the researchers advise.