Marijuana’s humid growing conditions encourage dangerous mold. States where marijuana is legal make growers hire laboratories to check for concentrations of mold and other contaminants that can sicken or kill. Labs in many states appear to underreport concentrations of contaminants, a Wall Street Journal analysis found. A disproportionate share of the samples were reported to contain levels of mold just under legal limits compared with the share of samples containing levels of mold just over legal limits, concluded the analysis of over two million mold-testing results from nine states. The improbable pattern suggests tainted samples are being cleared for sale, experts said. The findings show a system that isn’t reliably monitoring for dangerous substances in legal marijuana. “This is something that would not be expected if you took measurements of mold and reported them out in a way that was done without knowledge of the legal threshold,” said Joseph Hogan, a biostatistician at Brown University. Growers, labs and regulators appear to be exposing people who use legal marijuana to dangerous contaminants, said Tess Eidem of the Environmental Engineering Program at the University of Colorado, Boulder. “There’s no way to know what’s going on when you get a system that doesn’t play by the rules,” she said. The Journal sought mold-testing data from the 37 states with medical or recreational marijuana programs.
The newspaper got data from 18 states, ranging from 2014-2024. Molds including Aspergillus and Fusarium as well as the toxins they produce can cause infections, dangerous immune responses and even death. Marijuana users are nearly four times as likely as nonusers to be infected with fungi including Aspergillus, a review of insurance claims showed. Labs in Colorado, Massachusetts and Rhode Island were four times more likely to report results just under legal limits than just over. The cannabis-control commission in Massachusetts said environmental factors and different testing methods can produce atypical results. Rhode Island’s cannabis-control commission said it would welcome a nationwide standard for testing marijuana. Maryland in 2021 raised its legal limit by a factor of 10. Average mold concentrations reported by labs in the state increased in kind. Most states set the limit on yeast and mold content in cannabis at 10,000 “colony forming units” of yeast and mold per gram, a measure of cells that could form harmful growths. Labs use one of two tests: a lab culture or PCR testing.
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