After the increase in e-cigarette or vaping product use-associated lung injury (EVALI), researchers set out to explore how the added ingredients in cannabis vaping aerosols affect the product when consumed. After all, vaping mixtures for both sometimes included ingredients for cutting. One of these ingredients in e-cigarette oil, vitamin E acetate, and the subsequent formation of toxic ketene gas, was heavily linked with EVALI. [1,2]
In a study by Meehan et al., researchers studied how the ratios of delta-9-tetrahydrocannabinol (THC) to terpenes affected the amount of THC and harmful and potentially harmful chemicals (HPHCs) consumed including volatile organic compounds (VOCs) isoprene, methyl vinyl ketone, and methacrolein. They measured the ratios present when vaping and dabbing through the use of automated thermal desorption-gas chromatography-mass spectrometry as the thermal degradation mechanism.
The average amount of oxidation products, like isoprene, inhaled in indoor air typically causes humans no harm. However, when mice were exposed to terpene oxidation products in proportions similar to what humans inhale during a vaping session, they suffered from sensory irritation and limited airflow.  Hence, limiting the levels of VOCs that result from inhaling cannabis is best.
When dabbing a THC-β-myrcene mixture comprised of 5% β-myrcene-d6 (deuterated myrcene), the researchers found that terpenes were responsible for 0.75% of the isoprene formed. Notably, THC only produced 0.15% of isoprene. Additionally, higher levels of β-myrcene also led to augmented formation of methyl vinyl ketone and methacrolein.
Researchers believe the higher percentage of isoprene created from the terpenes could stem from the ease at which β-myrcene produces isoprene compared to THC. The easier production means less energy is necessary to generate isoprene. Additionally, β-myrcene’s particles are smaller than THC particles, leading to less molar heat capacity in β-myrcene. The smaller the capacity, the easier the bonds break.
The study authors also observed vaping to see how terpenes affect the delivery of THC. The results showed a significant increase in the THC transfer per puff (THCT) when using β-myrcene. Additionally, the researchers found that vaping synthetic cannabis oil (SCO) with 7.2% β-myrcene compared to vaping pure THC mixtures produced comparable levels of HPHCs. Also, the higher the percentage of β-myrcene, the fewer HPHCs, and, again, the more THC was delivered, pointing to a higher vaporizer efficiency with the highest terpene mass % tested.
The researchers pointed to a reduction in oil viscosity with increasing β-myrcene, as well as a lower boiling point. The decreased boiling point would concomitantly decrease the temperature needed to aerosolize the oil, meaning less chance for chemical degradation.
Overall, the study’s authors determined that a higher terpene content in cannabis oil when vaping stifles degradation and enhances the delivery of starting materials. Fewer HPHCs are delivered, and more THC is produced per puff. Conversely, an opposite effect was found for dabbing, where higher levels of β-myrcene produced higher levels of HPHCs.
References Meehan-Atrash J, Luo W, McWhirter KJ, Dennis DG, Sarlah D, et al. The influence of terpenes on the release of volatile organic compounds and active ingredients to cannabis vaping aerosols. RSC Advances. 2021;11:11714-11723. [journal impact factor = 3.36; times cited = 0]
 Wu D, & O’Shea DF. Potential for release of pulmonary toxic ketene from vaping pyrolysis of vitamin E acetate. Proceedings of the National Academy of Sciences of the United States of America. 2020;117:6349-6355. [journal impact factor = 11.2; times cited = 59]