Does Heating in a Vaporizer Reduce the Microbial Load in Cannabis?

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There is currently an ongoing discussion about the microbiological quality requirements for medical Cannabis depending on the route of administration. In this context, certain microbial requirements were proposed  in the USP HMC draft Cannabis monograph published last year. These include, e.g., requirements for oral use, more strict requirements for inhalation use, as well as special requirements for vulnerable user groups, such as immunosuppressed patients. However, there are currently no specific microbial limits provided in the Ph. Eur. draft monograph for Cannabis flower. To move forward authors from the FDA recently published an article about a microbiological study of bulk Cannabis in the Journal Frontiers in Cellular and Infection Microbiology (13 January 2023, Volume 12 - 2022).

What is the impact of heating in a vaporizer on the microbiological quality?

By administration by inhalation Cannabis is usually heated in a vaporizer, vaporized and/or aerosolized, and inhaled. "Heating to high temperatures is known to kill microorganisms including bacteria and fungi; however, microbial death is dependent upon exposure time and temperature" the authors of the article say. And: "It is unknown whether the heating of cannabis at temperatures and times designated by a commercial vaporizer utilized in clinical settings will significantly decrease the microbial loads in cannabis plant material".

For conducting the study to assess this question, Cannabis test materials was used (i.e., dried cannabis plant materials were supplied as unfiltered cigarettes). Three types of cannabis material were used in the study: placebo without measurable THC, low potency containing 1.90% delta-9 THC, and high potency containing 6.50% delta-9 THC.

The authors finally conclude the following:

• Heating of the cannabis materials using standard vaporization parameters of 70 seconds at 190°C (settings suggested by the manufacturer) did not lead to significant reductions of the existing microbial bioburden.
• The findings demonstrate that heating with a vaporizer may not be considered effective to limit microbial risks associated with inhaled cannabis use.
• Other decontamination methods, such as gamma irradiation, ultraviolet germicidal irradiation or pasteurization may thus be needed to limit microbial contamination in Cannabis.

For more information please see the article Investigation of microorganisms in cannabis after heating in a commercial vaporizer published in Frontiers in Cellular and Infection Microbiology.