The Institute of Medicine's Mar. 1999 Report stated on page 113:

“Results of human studies suggest that there is a greater chance of respiratory illness in people who smoke marijuana…

When marijuana smokers were compared with nonsmokers and tobacco smokers in a group of 446 volunteers, 15-20% of the marijuana smokers reported symptoms of chronic bronchitis, including chronic cough and phlegm production…Habitual marijuana smoking is associated with changes in the lining of the human respiratory tract.

Many marijuana or tobacco smokers have increased redness (erythema) and swelling (edema) of the airway tissues and increased mucous secretions.”

Mar. 1999 - “Marijuana and Medicine: Assessing the Science Base”