The risks of vaping cannabis
A year ago, there was a lot of talk about the risks of vaping cannabis (THC containing liquids) – media reporting ‘vaping-related lung illnesses’ across America. Vaping was mistaken for vaporization, a medical device for administering cannabis flos,  and was considered dangerous. In our 2019 article, we discussed the risks of using ‘vape-pens’,  their diluents or carrier agents,   and the accompanying socially intrusive vapour clouds. None of which are a feature of the medicinal use of cannabis flos by vaporization. 
So, what has happened since then?
The vaping saga
To recap. Vaping works by heating a liquid (i.e. cannabinoids and diluents) to produce an aerosol that is inhaled into the lungs.  In 2019, a surge of people with vaping associated pulmonary injury, some cases fatal, had many scratching their heads looking for answers.
The serious incidents in the United States of ‘E-cigarette, or Vaping, product use-Associated Lung Injury’ (EVALI) were investigated by the US Centres for Disease Control and Prevention (CDC), Food and Drug Administration (FDA) and clinical partners.  Their investigations continue into 2020.
The CDC goes on to state that, “informal sources are linked to most EVALI cases and play a major role in the outbreak”. Indeed, the link to Informal sources, likely illegal and counterfeit products, produced and distributed without regulatory oversight, is substantiated by a report by Anresco Laboratories (California, USA). Anresco tested legal and illegal samples in the state. They discovered no evidence of vitamin E acetate adulteration in the regulated-market products, and a high degree of vitamin E acetate contamination in illicit market samples. 
In response to the EVALI incident, the ASTM D-37 subcommittee, a cannabis industry standards-setting organisation, discussed vaping concentrates (February 2020, Atlanta, GA, USA). The dialogue included that diluents used in formulating liquids for vaping should be exposed to high temperatures and screened for toxic by-products. This would help assure that no harmful constituents are incorporated into regulated cannabis vape products, now and into the future.
Clearly, industry engagement, robust regulatory processes, and active enforcement remain the backstop to challenge illegal activity in any market.
Various risks of vaping cannabis
Nonetheless, while the legal cannabis market appears sound, there remain various risks of vaping cannabis. There is money made in illegal sales. Counterfeit vape materials and packaging have entered the legal market, at least in California (USA).   The unregulated cannabis flower used to produce concentrates is often found to contain higher levels of pesticides, heavy metals, and other contaminants. And, importantly, the process of producing cannabinoid concentrates will logically lead to exposing consumers to higher concentrations of a wide range of toxins.
Given the pace of development in regulated markets, we may see a sizable proportion of consumers continue to source products from unregulated sources. At least in the short term. This is evident even in Canada, a nationally regulated market, where not everyone obtains their cannabis from legal, quality-assured sources.  In this frame, harm caused by the consumption of unregulated products will continue and so will the risks of vaping cannabis.
So, the issue of vaping associated pulmonary injury is by no means resolved. The black market appears to be at fault. Meanwhile, the various regulators remain vigilant. And, the industry appears resolute in upholding obligatory quality standards.
 Fully-standardised, pharmaceutical-quality cannabis flos is the whole, dried flowers/inflorescence of the cannabis plant, which is genetically and chemically standardised according to pharmaceutical standards. It is free of contaminants such as microbial contaminants (molds, fungi, and bacteria) pesticides (residues), aflatoxins, impurities and heavy metals.
 Douglas, H., Hall, W., Gartner, C. (2015). E-cigarettes and the law in Australia. Australian Family Physician. 44 (6): 415-418.
Jensen, P., Luo, W., Pankow, J., Strongin, R., Peyton, D. Hidden formaldehyde in e-cigarette aerosols. New England Journal of Medicine. 372 (4): 392-393.
Editorial and Review (2019). E-Cigarettes and vaping-related disease. New England Journal of Medicine.
 A variety of diluents, which act as carrier agents, have been used in vape pens, including Polypropylene Glycol (PPG), Propylene Glycol (PG), Polyethylene Glycol (PEG), Vegetable Glycerin (VG), and Ethylene Glycol (EG).
Given the associated health risks with the consumption of the above-noted diluents, vaporizer cartridge producers seem to be moving towards using terpenes, or alternative extraction methods which produce a less viscous cannabis concentrate, eliminating the need for diluents altogether.
 Troutt, W., and DiDonato, M. (2017). Carbonyl compounds produced by vaporizing cannabis oil thinning agents. J Altern Complement Med. 2017 Nov;23(11):879-884.
 Eisenberg, E., Ogintz, M., Almog, S. (2014). The pharmacokinetics, efficacy, safety, and ease of use of a novel portable metered-dose cannabis inhaler in patients with chronic neuropathic pain: A Phase 1a study. Journal of Pain & Palliative Care Pharmacotherapy. 28:216–225.
Hazekamp, A., Ruhaak, R., Zuurman, L., van Gerven, J., Verpoorte, R. (2006). Evaluation of a vaporizing device (Volcano) for the pulmonary administration of tetrahydrocannabinol. Journal of Pharmaceutical Sciences. 95(6):1308-17.
 A vape pen (an atomiser vaporiser) is a device typically containing an electronic heating system and a cartridge (containing a cannabis-based liquid (i.e. decarboxylated cannabinoids and excipients (a diluent or carrier agent)). The liquid is heated, creating an aerosol vapour which is inhaled via a mouthpiece.
 CDC update (25 February 2020). ‘Outbreak of Lung Injury Associated with the Use of E-Cigarette, or Vaping, Products’
 Blount, B., Karwowski, M., Shields, P., et al. (2020). Vitamin E acetate in bronchoalveolar-lavage fluid associated with EVALI. N Engl J Med 2020; 382:697-705.
 Eisenberg, Z., Moy, D., Lam, V., Cheng, C., Richard, J., Burack, B. (26 October 2019). Contaminant analysis of illicit vs regulated market extracts. Anresco Laboratories.
 Queally, J. (2019). Counterfeit cannabis products stoke black market for California weed. Los Angeles Times; 26 August, 2019.
 Eisenberg, Z., Moy, D., Lam, V., Cheng, C., Richard, J., Burack, B. (26 October 2019). Contaminant Analysis Of Illicit Vs Regulated Market Extracts; Anresco Laboratories.
 Dryburgh, L., Bolan, N., Grof, C., Galettis, P., Schneider, J., Lucas, C., Martin, J. (2018). Cannabis contaminants: sources, distribution, human toxicity and pharmacologic effects. Br J Clin Pharmacol. 2018 Nov; 84(11): 2468–2476.
 Health Canada (2019). The Canadian Cannabis Survey 2019