California’s Office of Environmental Health Hazard Assessment (OEHHA) added four substances — hydrochlorothiazide, voriconazole, tacrolimus, and welding fumes — to the Proposition 65 carcinogen list, triggering warning-label obligations for businesses one year from the listing date.
What Happened
On July 17, 2026, OEHHA issued a notice listing three pharmaceuticals (hydrochlorothiazide, a diuretic; voriconazole, an antifungal; tacrolimus, an immunosuppressant) and welding fumes as known carcinogens under Proposition 65 (the Safe Drinking Water and Toxic Enforcement Act).
What’s New
- Hydrochlorothiazide (HCTZ) — widely used diuretic for hypertension and edema — added as a carcinogen.
- Voriconazole (VRCZ) — broad-spectrum antifungal for invasive fungal infections — added as a carcinogen.
- Tacrolimus (TAC) — post-transplant immunosuppressant — added as a carcinogen.
- Welding fumes — metal oxide particle mixtures generated during welding — added based on epidemiological evidence of increased lung cancer risk.
Key Dates & Compliance Deadlines
Four substances added to the Proposition 65 carcinogen list.
One-year grace period expires; warning obligations begin.
20-month compliance deadline for emission control measures.
Affected Industries
Pharmaceutical manufacturers and distributors (three listed drugs); welding, metal fabrication, shipbuilding, and construction industries (welding fumes); any business with California operations, products, or emissions involving these substances.
Who Is Affected
Any business operating in California whose products, premises, or emissions contain these substances above the applicable safe-harbor threshold, including manufacturers, employers with welding operations, and rental housing/workplace operators.
Substances / Products in Scope
Hydrochlorothiazide, voriconazole, tacrolimus (pharmaceuticals); welding fumes (metal oxide particle mixtures).
Prohibitions, Restrictions & Exemptions
Businesses must provide clear and reasonable cancer warnings (labels, workplace postings, rental notices, or newspaper announcements) once the one-year grace period lapses; discharge of these substances into potential drinking water sources is prohibited, with a 20-month window to implement emission controls.
What Companies Should Do
- Identify products, workplaces, or emissions involving hydrochlorothiazide, voriconazole, tacrolimus, or welding fumes.
- Prepare Proposition 65 warning labels/postings ahead of the one-year compliance deadline (July 17, 2027).
- Assess and implement emission control measures for any relevant water discharge pathways within 20 months.
- Query updated Proposition 65 substance status tools for affected CAS numbers.
Welding fumes carry the broadest cross-industry impact of this listing — metal fabrication, construction, shipbuilding, and automotive manufacturing operations with welding processes in California should begin warning-label and workplace-posting preparations well ahead of the one-year deadline.
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