On the other hand, THC and other cannabinoids are not water soluble, permitting them to pass through water to be inhaled. While tars and particulate matter are not water soluble, water nevertheless does seem to retain some of them. Therefore, when marijuana smoke is filtered through a water medium, some of the cannabinoids will be filtered out along with the tars to which they are chemically bonded. The key question is whether the tars will be selectively filtered out to a greater degree than the cannabinoids, resulting in a smoke that has a higher proportion of cannabinoids than before it passed through the water. If the cannabinoids and tars are filtered out equally, smokers will still end up inhaling the same proportion of each to reach the desired therapeutic levels of the cannabinoids.
Water pipes do reduce the temperature of the smoke.
Since heat is an important co-factor for carcinogenicity, water pipes offer at least this safety advantage. Vaporizers theoretically permit the cannabinoids to be inhaled virtually without any tars and particulate matter. Vaporizers work by heating the marijuana to a temperature at which the cannabinoids boil out from the marijuana, creating a vapor that can be inhaled. The temperature at which the cannabinoids turn to vapor is below that at which the marijuana leaf combusts, so there are presumably few or no combustion products such as carbon monoxide and tars. This is the theory this study will put to the test.