As pro-cannabis laws sweep the country, new opportunities are created for patients seeking medicinal cannabis. However, those with comprised immune systems need to be especially cautious about what they put into their bodies.
Cannabis flowers carry bacteria and fungi. These microorganisms can trigger an immune response. A study published in Supportive Care in Cancer looked at three sterilization methods to determine the best way to prepare cannabis flower for consumption by immunocompromised patients.  In particular, the study authors examined the case of a young man suffering from chemotherapy-induced pain and nausea. The taste of cannabis-infused edibles exacerbated his nausea.
Before allowing the patient to inhale cannabis smoke or vapor, the authors note that his medical team was concerned that “this may directly infect his lungs with potentially virulent pathogens…” To obviate the concern, the patient’s cannabis was first cultured to see if any microorganisms were present. The resulting culture generated Aspergillus (a fungi that can cause fatal infection in the immunocompromised). When the contaminated cannabis was subsequently sterilized, beneficial compounds like delta-9-tetrahydrocannabinol (THC) degraded.
The researchers recognized the need for a balance between sterilization and THC loss. Smoking or vaping untreated cannabis flower obviously doesn’t sterilize the biomass for consumption by the immunocompromised. Of the three methods studied — plasma, autoclave, and ethylene oxide gas — the researchers determined that plasma sterilization was the most effective at meeting both goals: sterilization and preserving THC, although they still saw a 12.6% reduction in THC activity.
Plasma sterilization works by oxidation. Liquid hydrogen peroxide is heated until it becomes plasma. The hydrogen peroxide molecules turn into free radicals that clamp onto microorganisms, essentially killing them.
Autoclave sterilization takes advantage of steam. The flower is exposed to high-temperature, high-pressure steam within an autoclave, a device that resembles a pressure cooker. According to the Centers for Disease Control and Prevention (CDC): “two common steam-sterilizing temperatures are 121°C (250°F) and 132°C (270°F).”
Ethylene oxide sterilization relies on manipulating four variables: time, temperature, humidity, and gas concentration. Ethylene oxide (EO) is a flammable, colorless gas. Cannabis is placed in a vacuum and exposed to EO. The exposure prevents microorganisms that may be on the flower from reproducing.
Sterilization matters because, as the study authors emphasize, there is a serious “hazard involved in smoking or vaporization of medicinal cannabis for immunosuppressed patients…” Infused edibles don’t present the same risk, but patients may find that it augments their nausea. 
Image source: Health Europa
- Ruchlemer, Rosa, et al. “Inhaled Medicinal Cannabis and the Immunocompromised Patient.” Support Care Cancer, September 2014, doi:10.1007/s00520-014-2429-3. Journal Impact Factor = 2.754, Times Cited = 24