Some critics exaggerate the dangers of marijuana smoking by fallaciously citing a study by Dr. Tashkin which found that daily pot smokers experienced a “mild but significant” increase in airflow resistance in the large airways greater than that seen in persons smoking 16 cigarettes per day.1 What they ignore is that the same study examined other, more important aspects of lung health, in which marijuana smokers did much better than tobacco smokers. Dr. Tashkin himself disavows the notion that one joint equals 16 cigarettes.
A more widely accepted estimate is that marijuana smokers consume four times as much carcinogenic tar as cigarettes smokers per weight smoked.2 This does not necessarily mean that one joint equals four cigarettes, since joints usually weigh less. In fact, the average joint has been estimated to contain 0.4 grams of pot, a bit less than one-half the weight of a cigarette, making one joint equal to two cigarettes (actually, joint sizes range from cigar-sized spliffs smoked by Rastas, to very fine sinsemilla joints weighing as little as 0.2 grams). It should be noted that there is no exact equivalency between tobacco and marijuana smoking, because they affect different parts of the respiratory tract differently: whereas tobacco tends to penetrate to the smaller, peripheral passageways of the lungs, pot tends to concentrate on the larger, central passageways.3 One consequence of this is that pot, unlike tobacco, does not appear to cause emphysema.
