Cannabis smoking causes a markedly higher respiratory burden of CO and tar compared to tobacco.
Summary
n=15 men with long-term cannabis and tobacco use (≥5 years); cannabis smoking vs. tobacco: ~5-fold higher increase in blood carboxyhemoglobin, ~3-fold more inhaled tar, 1/3 more tar retention in the respiratory tract (p<0.001); puff volume ~2/3 larger, inhalation depth 1/3 greater, breath-hold duration ~4-fold longer (p<0.01) — independent of THC content. Increased respiratory pollutant burden (carbon monoxide, tar); a direct cancer risk is not demonstrated.
P
PopulationMen who had smoked both cannabis and tobacco for at least 5 years, n=15
I
InterventionSmoking of cannabis cigarettes (741–985 mg, 0,004% or 1,24% THC)
C
ControlSmoking of filter-tipped tobacco cigarettes (900–1200 mg)
O
OutcomeCannabis smoking associated with ~5-fold increase in carboxyhemoglobin level, ~3-fold increase in inhaled tar amount and ~1/3 higher tar retention in the respiratory tract vs. tobacco (p<0,001)
Confidence in the evidence
Very lowLowModerateHigh
Very low
The lowest GRADE level, the effect estimate remains uncertain.
To compare the pulmonary hazards of smoking Cannabis and tobacco, we quantified the relative burden to the lung of insoluble particulates (tar) and carbon monoxide from the smoke of similar quantities of Cannabis and tobacco. The 15 subjects, all men, had smoked both Cannabis 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 Cannabis cigarettes (741 to 985 mg) containing 0.004 percent or 1.24 percent delta 9-tetrahydrocanabinol. As compared with smoking tobacco, smoking Cannabis 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 less than 0.001). Significant differences were also noted in the dynamics of smoking Cannabis 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 Cannabis than with tobacco (P less than 0.01). Smoking dynamics and the delivery of tar during Cannabis smoking were only slightly influenced by the percentage of tetrahydrocanabinol. We conclude that smoking Cannabis, regardless of tetrahydrocannabinol content, results in a substantially greater respiratory burden of carbon monoxide and tar than smoking a similar quantity of tobacco.