To this day, a proliferation of even more highly-concentrated cannabis e-cigarettes or CECs continue to roll-out in legal and black markets. Investigations by the New York Department of Health and the US Food & Drug Administration determined in 2019 that e-cigarette or vaping product use associated lung injuries (EVALIs) are mostly a result of counterfeit CECs with large concentrations of vitamin E acetate (VEA) and various other toxic compounds affecting the bronchoalveolar lavage fluids of patients suffering from the acute lung disease.
To further expound on those findings, researchers at the University of Rochester Department of Environmental Medicine analyzed chemical composition and pulmonary toxicology data on five types of CEC compositions and came away with the following :
Delta-9-tetrahydrocannabinol (THC), Terpenes/Flavorants – Researchers are mostly restricted from accessing these types of products for their studies because of the complex legality of delta-9-THC, however aerosols from these types are known to contain approximately double the amount of delta-9-THC compared to cannabis smoke. It still isn’t known what effect this may have on the respiratory system.
Delta-8-THC, Delta-10-THC, Terpenes/Flavorants, Cutting Agents/Viscosity Modifiers –
The chemical conversion of hemp-based cannabidiol (CBD) into compounds like delta-8-THC and delta-10-THC requires a final purification sequence that not all CEC manufacturers utilize to remove any remaining cytotoxic chemicals like sulfuric acid, hydrochloric acid, trifluoroacetic acid, or p-toluenesulfonic acid. Many of these products contained residual solvents and heavy metals as well.
CBD, Cannabichromene (CBC), Cannabicyclol (CBL), and Cannabicitran (CBT), Terpenes/Flavorants – Non-intoxicating CBD vaporizers – which often include other cannabinoids such as CBC and CBL – require more additives to produce viscous oils that can be vaporized since CBD quickly crystallizes at higher purities. These additives often include terpenes or propylene glycol (PG), the latter of which can wind up contributing heavily to bronchial tissue damage.  Inhalation toxicology data for these types of CECs still remains sparse.
Delta-9-THC, CBD, Terpenes/Flavorants, Cutting Agents/Viscosity Modifiers – Initial and subsequent studies regarding EVALI beginning in 2019 revealed these counterfeit CECs to contain high levels of VEA, squalene (a triterpene), phytol (a terpenoid), medium chain triglycerides oil, and compounds that are harmful if inhaled. The prohibition of VEA by many states as an additive has seen a drop in EVALI cases, however there still remains the possibility of numerous other hazardous additives in these devices, legal or not.
CBD, Flavorants, PG, Glycerol – Primarily found in electronic nicotine devices, these products contain PG and glycerol and typically contain fruit, candy, or menthol flavors. One study reported that the terpenes linalool, dipentene (racemic limonene), and citral found in some CECs were the most radical-generating molecules of all flavorants found.  Their exposure to high temperatures when vaped is also noted as a potentially significant factor.
When data of these five types of CECs is examined as a whole, it can be determined that several types of CECs can cause symptoms associated with acute lung injuries and EVALI, but also exemplifies the difficulty in determining further toxicological impacts in association with inhaling vapor containing unknown components and adulterants. The researchers of this study concluded that along with “a deep focus on cannabis industry innovations and user trends, researchers will have to fabricate products for themselves that fit within the parameters of similar such studies” – a necessary enterprise to sidestep non-access to legal CECs found in many states that are at the root of these health concerns.
Reference Meehan-Atrash J, Rahman I. Cannabis vaping: Existing and emerging modalities, chemistry, and pulmonary toxicology. Chem Res Toxicol. 2021;34(10):2169-2179. [journal impact factor = 3.739; times cited = N/A]  Bitzer ZT, Goel R, Reilly SM, et al. Effect of flavoring chemicals on free radical formation in electronic cigarette aerosols. Free Radic Biol Med. 2018;120:72-79. [journal impact factor = 7.376; times cited = 83]  Meehan-Atrash J, Rahman I. Cannabis vaping: existing and emerging modalities, chemistry, and pulmonary toxicology. Chemical Research in Toxicology. 2021;34 (10), 2169-2179 . [journal impact factor = 3.739; times cited = 5]