Recent scientific research has raised concerns about a possible link between the widely prescribed blood pressure medication hydrochlorothiazide (HCTZ) and an increased risk of certain types of skin cancer. The evidence suggests that prolonged use of this drug may be associated with a higher likelihood of developing malignant melanoma, squamous cell carcinoma of the lip, and other non-melanoma skin cancers, particularly among older adults. While experts strongly advise patients not to stop taking the medication abruptly, they emphasize the importance of greater awareness, careful monitoring, and effective sun protection.

Unveiling the Link Between Hydrochlorothiazide and Skin Cancer

Hydrochlorothiazide is one of the most commonly prescribed antihypertensive drugs worldwide and belongs to the class of thiazide diuretics. It has been used for decades to manage high blood pressure and reduce the risk of cardiovascular complications. However, emerging research indicates that HCTZ has photosensitizing properties, meaning it increases the skin’s sensitivity to ultraviolet (UV) radiation. This heightened sensitivity may make skin cells more vulnerable to UV-induced DNA damage, a key factor in the development of skin cancer.

A major study led by researchers at UNSW Sydney has strengthened evidence of this association. Using large-scale health and prescription data, the researchers identified a clear link between hydrochlorothiazide use and an elevated risk of lip cancer and malignant melanoma among older Australians. Given Australia’s high ambient UV exposure and globally high skin cancer rates, the findings are particularly significant.

Key Findings at a Glance

• Hydrochlorothiazide use is associated with an increased risk of malignant melanoma and squamous cell carcinoma of the lip.

• The risk of lip cancer appears to be cumulative, rising with longer duration and higher total exposure to HCTZ.

• Among commonly used blood pressure medications, HCTZ is considered the most phototoxic.

• Other classes of antihypertensive drugs did not show a similar increase in skin cancer risk.

• Experts caution that patients should not discontinue HCTZ suddenly without medical advice.

What the Research Shows

The UNSW Sydney study analyzed skin cancer rates in older individuals and compared hydrochlorothiazide use among patients diagnosed with lip cancer or malignant melanoma against matched control groups. The analysis adjusted for confounding factors, including other medications and levels of environmental UV radiation, strengthening the reliability of the results.

These findings align with international research. A large population-based study published in the Canadian Medical Association Journal (CMAJ) by researchers at the University of Toronto followed nearly one million adults aged 66 and older over a 20-year period. The study found that long-term HCTZ use was associated with a 34% increased risk of melanoma. While the increased risk of keratinocyte carcinoma was more modest (around 8%), melanoma is a far more aggressive and potentially fatal form of skin cancer, making the findings clinically important.

Earlier studies from Denmark, the United Kingdom, and the United States have reported similar dose-dependent associations, suggesting that the link is not limited to a single population or healthcare system.

Expert Guidance for Patients and Clinicians

Dr. Benjamin Daniels, lead author of the UNSW Sydney study, stresses that these findings should not cause panic or prompt patients to stop their medication without guidance. High blood pressure remains a serious condition, and poorly controlled hypertension significantly increases the risk of heart attack, stroke, and kidney disease.

Instead, healthcare professionals are encouraged to:

• Conduct more frequent skin examinations for patients taking HCTZ long term

• Reinforce sun-safe behaviors, including regular sunscreen use, protective clothing, and avoiding peak UV hours

• Discuss alternative antihypertensive options with patients who have a history of skin cancer or are at particularly high risk

Regulatory authorities have also responded. Product information for medications containing hydrochlorothiazide has been updated in several countries to include warnings about potential skin cancer risk. In Australia, the Therapeutic Goods Administration (TGA) advises patients with concerns to consult their healthcare provider rather than altering treatment on their own.

Global Significance and Future Directions

The confirmation of this association in Australia—a country with exceptionally high UV exposure—underscores its global relevance. Researchers hope future studies will include younger populations and more diverse demographic groups to better understand long-term risks and refine clinical guidance.

Ultimately, these findings highlight the need to balance the well-established cardiovascular benefits of hydrochlorothiazide with emerging evidence of potential dermatological risks. With informed prescribing, proactive sun protection, and regular skin monitoring, many patients may continue to use the medication safely while minimizing added risk.