Is irradiation enough to sanitize cannabis? A Canadian study casts doubt

L’gamma irradiation is now widely used in the production of medical marijuana to reduce the microbial load of dried flowers. This method, intended sterilize products before they are put on the market, is now being called into question by a McGill University study, published in late 2025 in the scientific journal Toxins.

Researchers have shown that while irradiation greatly reduces detectable bacteria and molds, it does not totally eliminate some of them. toxigenic fungi, nor mycotoxins they produce. This is a cause for concern, particularly for people with weakened immune systems.

From health risks underestimated

According to the research team viable spores belonging to well-known genera such as Aspergillus, Penicillium or Fusarium persist after irradiation. These fungi are capable of producing dangerous toxins, such as aflatoxins, the ochratoxins or the deoxynivalenol (DON).

However, nearly 70% of cannabis is consumed by inhalation, This allows the spores and residues to penetrate directly into the lungs. The study points out that cases of pulmonary mycoses have been documented in both immunocompromised patients and healthy consumers.

«It only takes one viable spore to cause disease, so we had to push the analysis beyond the limits of the ELISA test,» points out Saji George, co-author of the study.

From inadequate control methods

To assess contamination, the researchers analyzed non-irradiated flowers, irradiated flowers and flowers from authorized producers, by combining three approaches: microbiological cultures PCR/qPCR to detect fungal DNA, and analysis ELISA to quantify toxins.

The result: even when products comply with Canadian regulatory thresholds for yeast and mold, and traces of fungal DNA and residual mycotoxins remain detectable. The authors believe that the tests currently used in the industry can underestimate the real risks, They do not systematically detect viable spores.

«Standard state-of-the-art analytical methods [...] are unable to detect live spores,» warns the McGill team.

Prevention and hygiene, key levers

Faced with these limitations, researchers insist on the importance of prevention, rather than just sterilization at the end of the chain. Cannabis flowers, rich in resins, provide a particularly favorable environment for the development of fungi.

«Cannabis flowers contain sticky resins that greatly promote contamination,» explains Mamta Rani, co-author of the study. She emphasizes the need for increased vigilance at every stage, from cultivation to storage.

However, some companies are able to produce flowers that are virtually free of contamination thanks to controlled environments and strict hygiene protocols. The McGill team is also working with industry to explore biological solutions, such as the use of beneficial bacteria to limit fungal growth.

The authors do not argue in favor of rejecting irradiation, but rather in favor of evolving safety standards, particularly for the medical cannabis. They call for controls combining cultural, molecular and immunological analyses, to better protect the most vulnerable consumers.

«We're not looking to tarnish the industry's image, but to ensure its viability and provide guidelines for the production of safe products,» concludes the CEO. Saji George.