Ted Sarafian, PhD, Associate Research Scientist of Pulmonary and Critical Care Medicine in the Department of Medicine at the University of California at Los Angeles (UCLA) David Geffen School of Medicine, et al., wrote in their June 1999 study "Oxidative Stress Produced by Marijuana Smoke" in the American Journal of Respiratory Cell and Molecular Biology:

“Marijuana (MJ) smoking produces inflammation, edema, and cell injury in the tracheobronchial mucosa of smokers and may be a risk factor for lung cancer…

We conclude that MJ [marijuana] smoke containing Delta-9-THC is a potent source of cellular oxidative stress that could contribute significantly to cell injury and dysfunction in the lungs of smokers.”

June 1999