Request a Demo
Effective July 17, 2026, the California Office of Environmental Health Hazard Assessment (OEHHA) officially added hydrochlorothiazide, voriconazole, tacrolimus, and welding fumes to the Proposition 65 list of chemicals known to the state to cause cancer. The regulatory process was initiated with a Notice of Intent to List published in the California Regulatory Notice Register on May 8, 2026. A public comment period ran from May 8 to June 8, 2026, during which OEHHA received no comments.
The inclusion of these three chemicals was executed pursuant to the "Labor Code" listing mechanism (Health and Safety Code, section 25249.8(a); California Code of Regulations, title 27, section 25904). This statutory mechanism mandates that substances identified as human or animal carcinogens by the International Agency for Research on Cancer (IARC) be added to the Proposition 65 list.
It is worth noting that, with the exception of "welding fumes," which is classified as a process-generated risk, the other three pharmaceutical ingredients all have distinct CAS numbers corresponding to their chemical structures. These include hydrochlorothiazide (CAS RN 58-93-5), voriconazole (CAS RN 137234-62-9), and tacrolimus (CAS RN 104987-11-3). However, in this latest update to the official Prop 65 List, none of these four substances have been assigned specific CAS numbers.
It is not uncommon that Proposition 65 lists substances by their common names or as broad categories rather than by specific CAS numbers. This strict regulatory strategy is designed to broaden the scope of the law and prevent companies from bypassing warning requirements through minor chemical modifications (such as altering the salt or hydration state). This category-based listing approach is a well-established precedent in the Prop 65 list, frequently applied to substances like heavy metals, PFOS/PFNA, and phthalates.
With the effective listing date of July 17, 2026, affected entities—including manufacturers, distributors, and retailers dealing with products containing the aforementioned chemicals—must review their compliance obligations. Under Proposition 65, businesses are generally required to provide clear and reasonable warnings before knowingly and intentionally exposing Californians to listed chemicals. The complete, updated Proposition 65 chemical list reflecting these additions is available on the OEHHA website.
