Vaporization also plays an important role in using vaporizers (“vaping”) to deliver the cannabis APIs—cannabinoids and terpenes—from cannabis inflorescence. Ground inflorescence is heated in dedicated vaporizers for few minutes and the formed vapors are inhaled. In most vaporizers, the vapors are inhaled directly, while in others, the vapors are collected in a kind of a balloon and then inhaled from it. Many forms and designs of vaporizers exist on the market, with prices ranging from a few USD to almost 1000 USD. The recommended operation temperature is typically 160–220°C, or more specifically, about 180°C. This temperature is more than 200°C under the normal boiling points of THC and CBD.

Lanz et al.⁴⁶ have compared vaporization of cannabis in five commercial vaporizers, all of which were operated at 210°C for 3 min. Vaporization extent was 55–83% for THC and 46–70% for CBD. No data were provided for terpene vaporization. To compare terpene vaporization to that of cannabinoids, we have conducted a trial operating a Volcano vaporizer (one of the five used by Lanz et al.) at 180°C to 220°C, for durations extending from 20 to 180 sec.

Table 6 presents THCA, THC, and total THC concentrations before heating and in the residues after it. On temperature elevation, the acid form cannabinoids, for example, THCA and CBDA, decarboxylate to the neutral derivates, for example, THC and CBD. According to Table 6, at the conditions of the trial here, decarboxylation approaches completion within 40 sec at 180°C and is practically completed within 20 sec at 220°C.

Next, these neutral cannabinoids evaporate at a rate dependent on the operating temperature. Here, 34% and 50% of the THC evaporate within 20 and 40 sec, respectively, at 220°C, but only 10% and 20%, respectively, at 180°C, which is in good agreement with the corresponding vapor pressures. According to the Clausius–Clapeyron equation, compared with vaping at 160°C, the evaporation rate of THC at 180°C, 200°C, and 220°C are about 3 times, 8.4 times, and 19.4 times greater, that is, increasing by a factor of nearly 3 per 20°C of temperature elevation. Extrapolating the results in Table 6 shows that, at the conditions used here, at 180°C, more than 3 min are required for approaching complete evaporation of the THC.

Figure 3 presents the terpene content of the starting inflorescence and of that inflorescence after 20 and 40 sec at 180°C. Monoterpenes and monoterpenoids are mostly evaporated and the sesquiterpenes and sesquiterpenoids are markedly evaporated, before there is significant evaporation of THC. As can be concluded from Table 3, monoterpenes and monoterpenoids reach boiling at the temperature of vaporizer operation or approach it, whereas other terpenes have high vapor pressures, resulting in high rates of evaporation. Thus, for example, the rates of vaporization at 180°C of bisabolol (sesquiterpenoid), β-caryophyllene (sesquiterpene), linalool (monoterpenoid), and β-myrcene (monoterpene) are about 23, 380, 2200, and >3500 times greater compared with THC.

It is important to note that, while the data reported here applies to the composition of the vapors formed in the vaporizer, the composition of the inhaled vapors may differ. That is since the formed vapors cool down to some extent before being actually inhaled. On cooling, the cannabinoids (and possibly also some high-boiling terpenes) condense to small droplets. Those droplets may partially adsorb on the cooler parts of the vaporizer or stay within the balloon, when one is used. As a result, the proportion of the low-boiling terpenes in the actually inhaled vapors is even higher than that in the vaporizer-formed vapors.

These data and analysis show that, in using a vaporizer at recommended conditions, in total, the inhaled terpene to cannabinoid ratio is shifted away from that in the inflorescence. Potentially more importantly, the vast majority of the terpenes are inhaled before a significant fraction of the cannabinoids is received. It is not clear yet what the implications are of this time difference for the entourage effect.