Pot smoking contributes to lung disease

By Will Boggs, MD

NEW YORK (Reuters Health) - Long-term marijuana smoking significantly impairs lung function, according to a study published this month, which also found that smoking one cannabis joint has the adverse effects of up to five tobacco cigarettes.

"Habitual use of cannabis may cause asthma and chronic bronchitis," Dr. Richard Beasley from Medical Research Institute of New Zealand, Wellington, told Reuters Health. "The current initiatives to reduce tobacco smoking should also include attempts to reduce cannabis smoking."

Beasley and associates studied the lung health of 339 cannabis smokers, some of whom also smoked tobacco.

Cannabis smoking was associated with an increased risk of wheezing and coughing and feelings of tightness in the chest, they found, whereas tobacco smoking was associated with a similarly increased risk of wheezing and coughing.

Cannabis smokers had twice the risk of chronic bronchitis and a 70 percent increased risk of asthma diagnosed after age 16 years, they report in the medical journal Thorax.

Based on observed changes in lung function tests, the investigators calculate that one cannabis joint does as much harm as 2.5 to 5 tobacco cigarettes. "This provides patients with a good measure of the relative risks of cannabis and tobacco smoking," Beasley said.

"Although we know far less about the effect of cannabis on the lung than the effects of tobacco smoking, (this study) confirms that cannabis smoking constitutes a substantial hazard to the lung," comments Dr. Peter Lange from Hvidovre Hospital, Copenhagen, in a related editorial.

SOURCE: Thorax, December 2007.