Laboratories hired by states where marijuana is legally grown may not be correctly reporting the amount of mold and other dangerous contaminants found in the samples tested, according to an analysis by The Wall Street Journal.

Marijuana’s humid growing conditions are perfect for the growth of mold. According to a study published in Frontiers in Microbiology, the levels of yeast and mold in marijuana are regulated to ensure that medicinal and recreational users, especially those with compromised immune systems, are not exposed to harmful levels.

Now, the Journal investigators analyzed two million results from mold testing in nine states and found a large number contained levels of molds just over legal limits. This means that tainted samples are being sold and suggests the system isn’t sufficiently monitoring marijuana for dangerous substances.

Molds such as Aspergillus and Fusarium can cause serious infections, dangerous immune reactions and even death. A 2020 review found that people who take marijuana are nearly four times as likely as non-users to be infected with fungi.

Labs in Colorado, Massachusetts and Rhode Island were four times more likely to report test results just under the legal limits than just over, says the Journal. The limits on the amount of yeast and mold acceptable in marijuana differ, but most states set their limit at 10,000 colony-forming units per gram (CFU/g) to protect against harmful growth. Laboratories test marijuana samples either by culture or PCR tests.

Experts say that these measurements were modeled on the standards for other crops since there’s not a lot of research on growing marijuana. While several states allow the use of medical marijuana, it’s still federally illegal, and researchers have only begun to study the long-term effects of marijuana use.  

The state of Michigan stepped up its testing in February 2021 by requiring labs to have their testing methods validated by the nonprofit American Association of Official Agricultural Chemists. Samples analyzed in this manner showed excessive mold in 14% of the plant samples compared to 3% in previous testing. Other states have followed suit. This safety guard will help protect consumers, noted Claire Patterson, director of Michigan’s new reference lab.

According to Boveda, a company that studies humidity control for cannabis, another name for marijuana, moldy marijuana isn’t safe to consume or smoke. Depending on the type of mold present and the length of exposure, effects can be mild to severe and include coughing, trouble breathing, headaches, vomiting, diarrhea, heart palpitations and lung infections. People who have asthma or compromised immune systems are most likely to be affected by mold and the exposure could lead to death.

The moldy marijuana controversy is not new. Shockingly, in 2017 Anresco Laboratories analyzed an array of medical marijuana products from California-based growers and dispensaries and found 80% of them were tainted with mold, fungus, bacteria, pesticides and harmful solvents, according to San Francisco Magazine.

Patterson hopes that the marijuana industry will step up its vigilance in eradicating yeast and mold, as well as other contaminants.

“People selling products they know are contaminated don’t have a place in this industry if we want this industry to survive long-term,” she said.