Prescription drugs come with dozens of side effects. That’s normal. What’s unusual is when researchers discover a new side effect in a drug you’ve been taking regularly. Yet, that’s exactly what happened to a lot of people with high blood pressure.
A new study by researchers from UNSW Sydney found that hydrochlorothiazide, one of the most common drugs used for high blood pressure in Australia, increases the risk of skin and lip cancer. The results were especially worrying for older patients (aged 65 and over).
High blood pressure or hypertension is a condition characterized by having a blood pressure at or above 130/80 mm Hg. Hypertension leads to increased risks of strokes and heart attacks, and it’s been credited as the leading cause of death for around half a million Americans each year.
Higher risks of skin and lip cancer
The reason for this side-effect turns out to be pretty simple. Hydrochlorothiazide contains photosynthesizing properties that make our skin much more sensitive to the sun. This problem is especially significant for people living in sunny environments. Understandably, this discovery was made by scientists from Sidney.
The study was conducted through a big data analysis of skin cancer rates in a case-control study among older Australians. The results support similar findings from previous international studies (UK, Denmark, and the U.S.) that linked hydrochlorothiazide to an increased risk of skin cancer.
The lead author of the study was Dr. Benjamin Daniels, a pharmacoepidemiologist and a research fellow at the UNSW Medicine’s Centre for Big Data Research in Health (CBDRH).
In the study, the team used data from the Department of Veterans Affairs (DVA). It included de-identified information about cancer registrations, hospitalizations, and medicine dispensing for DVA healthcare cardholders (aged 65 and over) who lived in NSW between 2004 and 2015.
The researchers compared hydrochlorothiazide use in people who had been diagnosed with lip cancer (45 cases) or malignant melanoma (659 cases) compared with those with neither diagnosis (13,300 controls).
“We found an increased risk for developing malignant melanoma and squamous cell cancer of the lip (lip cancer) with hydrochlorothiazide use,” lead author Dr Benjamin Daniels said.
“For lip cancer, the risk also appears to be cumulative,” Dr. Daniels added. “That is, the longer that hydrochlorothiazide is used, the higher the risk of developing lip cancer.”
However, Dr Daniels cautioned strongly against stopping the popular medication without receiving medical advice from a doctor first, adding the skin cancer risk is something for prescribers and patients to be aware of.
“Hypertension is a condition that needs to be carefully managed,” says Dr. Daniels. “We don’t want anyone to suddenly stop taking hydrochlorothiazide out of fear of developing skin cancer.
“The skin cancer risk is something for prescribers to be aware of. Doctors may want to consider conducting more skin checks for their patients or reinforcing advice around sun-smart behaviors that everyone should be aware of, like adequate protection when UV is higher than three and avoiding sun exposure during peak UV times.”
Meanwhile, the manufacturers of hydrochlorothiazide have already gone on and updated the drug’s description to include this new side effect. Healthcare practitioners around the world are also being urged to acknowledge this new discovery and take it into consideration when prescribing hydrochlorothiazide.
“This [update] will help prescribers and patients to make informed choices about the benefits and risks of hydrochlorothiazide-containing medicines,” said a spokesperson from the Therapeutic Goods Administration in Australia (TGA).
“By informing physicians around the potential risk of skin cancer in Australia associated with this common treatment, we hope our findings can help improve the care of patients dealing with hypertension,” said Dr. Daniels.
As with so many other drugs with significant and often life-altering side-effects, researchers are already hard at work to look for better alternatives. In the meantime, it’s up to healthcare practitioners to determine in which cases of hypertension the prescription of hydrochlorothiazide is necessary despite the risks and in which – alternative methods can be pursued.
Even when hydrochlorothiazide is prescribed, however, the very least that can be done is to inform the patient of the new risks and instruct them on how to better protect themselves against skin and lip cancer.