In addition, marijuana smoking may increase risk of respiratory exposure by infectious organisms, such as fungi and molds, since cannabis plants are contaminated with a range of fungal spores, said Brent Moore, assistant professor of psychiatry at Yale School of Medicine and lead author of the study.
"Because more than two million adult Americans are heavy marijuana smokers, these risks represent a potentially large health burden," Moore said. "Marijuana smokers use more medical services for respiratory problems, and these demands are likely to increase as the population of heavy marijuana smokers ages."
The findings were based on 6,728 questionnaires completed by adult men and women, 20 to 59 years old, in 1988 and 1994. The data was from the National Health and Nutrition Examination Survey and was thought to provide the broadest snapshot to date of marijuana use and its effect on the lungs in a sample of U.S. citizens.
Current marijuana use was defined as self-reported lifetime use and use at least one day in the prior month. Seventy seven percent of marijuana smokers also smoked tobacco. The analysis statistically controlled for the number of cigarettes smoked per day. Individuals who smoked both marijuana and tobacco had increased rates of respiratory symptoms compared to those who smoked tobacco only.
"Our interest is in the additive effect of marijuana," Moore said.