Long-term marijuana smoking significantly impairs lung function. Also, smoking one cannabis joint has the adverse effects of up to five tobacco cigarettes.
Habitual use of cannabis may cause asthma and chronic bronchitis. Cannabis smoking increases the risk of wheezing and coughing accompanied by feelings of tightness in the chest, whereas tobacco smoking is associated with a similarly increased risk of wheezing and coughing.
Researchers from the Medical Research Institute of New Zealand, Wellington studied the lung health of 339 cannabis smokers, some of whom also smoked tobacco. It was found that cannabis smokers had twice the risk of chronic bronchitis and a 70 per cent increased risk of asthma diagnosed after the age of 16 years. Based on the changes observed in lung function tests, it was found that one cannabis joint does as much harm as 2.5-5 tobacco cigarettes. This provides patients with a good measure of the relative risks of cannabis and tobacco smoking.
Although less is known about the effect of cannabis on the lung than the effects of tobacco smoking, cannabis smoking constitutes a substantial hazard to the lung. The current initiatives to reduce tobacco smoking should also include attempts to reduce cannabis smoking