Reference summary — not medical advice or a personal risk estimate.
Hydrochlorothiazide
Quick answer
Classified as Group 1 — carcinogenic to humans, based on sufficient evidence in humans. Prescription medication. A common diuretic ("water pill") used to treat high blood pressure.
Summary
A common blood pressure medication associated with increased skin cancer risk.
Detail
IARC classified hydrochlorothiazide as Group 1, carcinogenic to humans, in 2024 (IARC Monographs Volume 137), based on sufficient evidence in humans for squamous cell carcinoma of the skin and for lip cancer. Evidence was limited for basal cell carcinoma, melanoma, Merkel cell carcinoma and other skin tumours. The proposed mechanism involves photosensitisation of the skin. Sun protection is a reasonable precaution for people taking it; questions about whether to continue or switch antihypertensive medication are clinical decisions between a patient and their care team.
What's not established
This classification is based on sufficient evidence in humans that this factor can cause cancer. It does not establish a safe exposure threshold, your personal risk, or how this factor's risk compares in size to other Group 1 agents — hazard classifications are not ranked by magnitude.
Regional relevance
global
Documented in these products
Presence in a product category doesn't imply the product causes cancer. Click each to see the source and context.
Evidence sources
Every claim on this page traces back to one of these. Click through to read the primary document yourself.
Primary sources
IARC
IARC Monographs — Classifications by Cancer Site, Vols 1–140
Supporting sources
ACS
ACS — Known and Probable Human Carcinogens
NTP
NTP — Report on Carcinogens (US National Toxicology Program)
Last reviewed: October 2026
Official reference list
A government list some readers use alongside the primary evidence. Meyron is not affiliated with it. A chemical being listed does not by itself describe a risk from any particular product.
- California Prop 65 list
State of California's list of chemicals known to cause cancer or reproductive harm.