Cryptococcal Meningitis: The Case Against Vaping Cannabis

“Medical and recreational cannabis has been shown to carry pathogenic fungi and bacteria.”

Kailey Hughes Kramer, PhD, Department of Medicine, Division of Infectious Diseases, University of Pittsburgh

“Contamination is not the only danger vaping weed poses.”

Deepak Cyril D'Souza, Professor of Psychiatry, Yale University

Minnesota established a medical cannabis program in 2014 and legalized cannabis for recreational use in 2023. This past fall that I noticed that a fancy cannabis shop (aka “pot” and “weed”) had popped up in my Minneapolis neighborhood. About that same time, the article “Medical Cannabis as the Source of Cryptococcus neoformans Infection” caught my eye. In this week’s post, I provide a summary of this life-threatening fungal infection and discuss what vaping of cannabis may have to do with this and other airborne fungal pathogens.

What is cryptococcal meningitis? Cryptococcus neoformans is a dimorphic fungus that exists primarily as a yeast in both the environment and human host. Its niche in the environment is in soil contaminated with bird droppings, particularly pigeon droppings.

The German pathologist Otto Busse discovered the pathogen in 1894 in a tibial bone lesion and called it Saccharomyces hominis. About the same time, Francesco Sanfelice cultured the yeast-like fungus from peach juice and named it Saccharomyces neofomans. It was later renamed Crypotcoccus neoformans—a term derived from a combination of Ancient Greek and Latin, reflecting its structural characteristics and its classification history. (Kryptos from the Ancient Greek meaning “hidden” and kokkos meaning “grain” refers to the organism’s large polysaccharide capsule, which effectively “hides” the yeast cell from the host’s immune system. Neoformans is from the Latin neo meaning “new” and formans meaning “shaping.” )

C. neoformans can infect almost any organ, but it has a strong predilection for the lungs and central nervous system. Infection typically begins in the lungs after the inhalation of environmental spores and can then spread through the bloodstream to other sites, especially the brain, where disease is manifest most commonly as meningitis.

Cryptococcal meningitis symptoms include severe headache, fever, stiff neck, nausea, vomiting, increased sensitivity to light, and confusion. Cryptococcal meningitis is treated with a combination of antifungal medications—a treatment that usually lasts at least six months. If left untreated, cryptococcal meningitis usually leads to more serious symptoms and ultimately death.

Who’s at risk? Cryptococcal meningitis is relatively uncommon in healthy people. (Some reports show that 10% to 30% of cases occur in people who are immunocompetent.) It is, however, a significant risk for immunocompromised patients, especially those with impaired cell-mediated immunity, such as transplant, cancer, and HIV/AIDS patients.

In the U.S., approximately 3,400 hospitalizations for cryptococcal infection occur annually, with organ transplantation and cancer being common risk factors. In sub-Saharan Africa, where the incidence of HIV/AIDS is high, it’s estimated there are more than 100,000 to 150,000 cases of cryptococcal meningitis annually. Mortality rates are also highest in this region—one year mortality is estimated at 70% or higher.

What are the proven benefits of medical marijuana (cannabis)? As of 2023, a broad range of medical marijuana products were legal in 38 states, three territories, and the District of Columbia but remained illegal under federal law. (Watson, S., Painter, K., “Medical Marijuana: Benefits and Side Effects,” WebMD, January 9, 2024). The U.S. Food and Drug Administration (FDA) has only approved three drugs related to cannabis, one to treat epilepsy and two to treat nausea and vomiting from chemotherapy and low appetite in HIV patients. The FDA has not approved any medical use of the cannabis plant itself or any of the many products made directly from the plant.

Cannabis is almost always used to treat symptoms rather than the underlying condition itself. Solid studies do suggest that cannabinoids, the active chemicals in medical marijuana, can control vomiting, modestly reduce pain, and reduce muscle spasms. But all other claims about the benefits of medicinal “weed” aren’t supported by properly controlled clinical trials. In other words, strong scientific evidence of the benefit of cannabis for many of its purported indications is lacking.

What are the health risks of cannabis vaping? Although most commonly used for nicotine, a wide range of devices are used to heat substances to create an aerosol which is then inhaled (vaped), such as is done in vaping of cannabis (medical marijuana). Vaping cannabis produces the quickest effects but it has its risks, including, but not limited to, inhaling pathogens. (The FDA has warned people not to vape marijuana products as they can cause lung damage.)

Several studies indicate that cannabis, particularly if improperly air dried, cured, or stored, can be heavily contaminated with mold, and these spores can survive the combustion process. Aspergillus, Mucorales, andFusarium, all airborne fungal pathogens, have been isolated from cannabis. And recently, researchers at the University of Pittsburgh, published the first study to definitely link an infection to a pathogen, C. neoformans, in medical cannabis used by a patient. (Kramer, K, et al., “Medical Cannabis as the Source of Cryptococcus neoformansInfection, Clinical Infectious Diseases, November 15, 2025).

The patient was a 46-year-old woman who had cancer (relapsing multiple myeloma) and died following a stem cell transplant. She had used medical cannabis for refractory chemotherapy-induced nausea. Whole-genome sequencing of C. neoformans from her epiglottis and cerebrospinal fluid and samples of the medical cannabis she used to control nausea were indistinguishable. Thus, this is the first study to definitively link an infection to a pathogen (C. neoformans) in medical cannabis.

What’s to be done? According to the WebMD article:  “Scientists who’ve reviewed medical marijuana research data say we need much more information on benefits and risks for individuals, as well as on the broader public health impact of wide availability.” The problem is that it is “hard to do studies on a drug that remains illegal under federal law, even when it’s allowed by states.”

In addition, funding cuts, grant terminations and freezes in 2025 and early 2026, have heavily impacted the National Institute of Drug Abuse, along with other NIH institutes and broader federal addiction research and treatment programs. Therefore, the prospects for increased research support, in general, as well as for psychoactive drugs, in particular, appear dismissal under the current leadership of this country.