Pulmonary Hazards of Smoking Marijuana as Compared with Tobacco

TLDR

The study compares the pulmonary hazards of smoking marijuana versus tobacco by quantifying the relative lung burden of tar and carbon monoxide from equivalent smoke quantities. Fifteen habitual male smokers of both substances were studied; their blood carboxyhemoglobin levels and tar deposition were measured before and after smoking single filter‑tipped cigarettes of comparable mass, with marijuana containing either 0.004% or 1.24% THC. Smoking marijuana produced a nearly five‑fold higher rise in blood carboxyhemoglobin, a three‑fold increase in inhaled tar, and a one‑third greater tar retention compared with tobacco, and involved larger puff volume, deeper inhalation, and longer breath‑hold; these effects were largely independent of THC content. Published in N Engl J Med 1988; 318:347–51.

Abstract

To compare the pulmonary hazards of smoking marijuana and tobacco, we quantified the relative burden to the lung of insoluble particulates (tar) and carbon monoxide from the smoke of similar quantities of marijuana and tobacco. The 15 subjects, all men, had smoked both marijuana and tobacco habitually for at least five years. We measured each subject's blood carboxyhemoglobin level before and after smoking and the amount of tar inhaled and deposited in the respiratory tract from the smoke of single filter-tipped tobacco cigarettes (900 to 1200 mg) and marijuana cigarettes (741 to 985 mg) containing 0.004 percent or 1.24 percent Δ9-tetrahydrocannabinol. As compared with smoking tobacco, smoking marijuana was associated with a nearly fivefold greater increment in the blood carboxyhemoglobin level, an approximately threefold increase in the amount of tar inhaled, and retention in the respiratory tract of one third more inhaled tar (P<0.001). Significant differences were also noted in the dynamics of smoking marijuana and tobacco, among them an approximately two-thirds larger puff volume, a one-third greater depth of inhalation, and a fourfold longer breath-holding time with marijuana than with tobacco (P<0.01). Smoking dynamics and the delivery of tar during marijuana smoking were only slightly influenced by the percentage of tetrahydrocannabinol. We conclude that smoking marijuana, regardless of tetrahydrocannabinol content, results in a substantially greater respiratory burden of carbon monoxide and tar than smoking a similar quantity of tobacco. (N Engl J Med 1988;318:347–51.)