On December 8, 2025, N-methyl-N-formylhydrazine (MFH) was added to the Prop 65 List as a carcinogen. As a result, the Prop 65 warning requirement for exposures to MFH will take effect on December 8, 2026. 

In its Evidence on the Carcinogenicity of N-Methyl-N-Formylhydrazine, OEHHA commented that MFH occurs naturally in edible wild Gyromitra mushrooms (which include those commonly referred to as spring false morels, false morels, or lorchels), and is used in the production of marbofloxacin (a fluoroquinolone antibiotic used in veterinary medicine) and for research purposes.

More information on the listing of MFH can be found here.