THC Transfer Rate

The MAPS-NORML study provides new information on the efficiency of different devices in delivering THC from marijuana to the user. Previous studies have shown that 60% - 80% of the THC burned in joints or waterpipes is lost in slipstream smoke, adhesion to the pipestem and bowl, pyrolysis, etc. [Mario Perez-Reyes, Marijuana Smoking: Factors that Influence the Bioavailability of Tetrahydrocannabinol, in C. Nora Chiang and Richard Hawks, ed., Research Findings on Smoking of Abused Substances, NIDA Research Monograph 99, 1990]. The percentage of total THC delivered to the user is called the THC transfer rate. The unfiltered joint scored surprisingly well in smoking efficiency, coming in second place with a transfer rate close to 20%. The portable waterpipe did slightly better, and the bong slightly worse. The other devices did notably worse. The vaporizers and electric waterpipe did especially poorly, with transfer rates less than one-third that of the top three devices. Thus, heavy smokers could literally be blowing most of their stash away with bad pipes.