Tar, CO and Δ⁹-THC delivery from the 1st and 2nd halves of a marijuana cigarette

Abstract

Previous in vitro studies suggest that, with successive puffs from a marijuana cigarette, delta-9-THC becomes concentrated in the remaining uncombusted portion of the cigarette. These observations are consistent with the common practice of smoking marijuana cigarettes to a smaller butt length than that to which tobacco cigarette. are smoked. The purpose of the present study was to compare the delivery of delta-9-THC, as well as total insoluble smoke particulates (tar) and carbon monoxide, from the distal (“first”) versus the proximal (“second”) halves of a standard marijuana cigarette during “natural” smoking of marijuana. On 4 separate days, ten habitual marijuana users smoked nearly all or approximately $\text{1}\text{2}$ of a standard marijuana cigarette (83 mm length; 800–900 mg; 1.24% THC), as follows: day 1, “whole” cigarette (60 mm smoked, leaving a 23-mm butt); day 2, “first” half (first 30 mm); day 3, “second” half (second 30 mm) after the “first” half was presmoked with a syringe; and day 4, “second” half after the “first” half was excised. A previously described smoking apparatus (20) was used for measurement of puff volume and inhaled tar. Puff volume and number were allowed to vary spontaneously (provided that the specified length of cigarette was consumed), while inhaled volume (1.5 liters), breathholding time (14 s) and interpuff interval (30 s) were held constant. Blood samples were withdrawn prior to smoking and serially after completion of smoking for analysis of blood carboxy-hemoglobin (COHb) and serum delta-9-THC. Heart rate was measured before and 5 min after smoking. Subjects rated their level of “high” 20 min after completion of smoking. Compared to the distal half, smoking the proximal half of a marijuana cigarette delivered more tar, carbon monoxide and THC to the smoker's lungs, as indicated by a greater amount of inhaled tar and a larger boost in both blood carboxyhemoglobin and serum THC. In addition, boosts in blood COHb and serum THC were significantly greater following smoking the proximal half after the distal half had been presmoked rather than excised. These findings are probably due to 1) less rod filtration of insoluble particulates, 2) increased concentration in the proximal half of the cigarette of carbonaceous material and THC volatilized by prior combustion of the distal half, and 3) possible differences in burn rate due to effects of precombustion of the distal half on moisture content of the proximal half. Clinical implications of these findings are that smoking fewer marijuana cigarettes down to a shorter butt length to deliver more THC and achieve a greater “high” is potentially more harmful to cardiorespiratory health than consuming a comparable amount of marijuana contained in more cigarettes smoked to a longer butt length.