Long term use of drugs that help lower high blood pressure may increase the risk of developing skin cancer, a study with nearly 80,000 participants has claimed.

Hydrochlorothiazide -- one of the most commonly used antihypertensive drugs worldwide -- is a thiazide diuretic (water pill) that helps prevent your body from absorbing too much salt, which can cause fluid retention.The findings revealed that using medicines that contain hydrochlorothiazide increases the risk of developing squamous cell carcinoma -- skin cancer that develops in the cells of the outer layer of the skin -- up to seven times."We knew that hydrochlorothiazide made the skin more vulnerable to damage from the sun's UV rays, but what is new and also surprising is that long term use of this blood pressure medicine leads to such a significant increase in the risk of skin cancer," said Anton Pottegard, associate professor at the University of Southern Denmark.

The researchers had previously demonstrated that hydrochlorothiazide can increase the risk of lip cancer.In the study, published in the Journal of the American Association of Dermatology, the team observed zero risk of skin cancer with other commonly used hypertension medicines.However, one should not interrupt the treatment without consulting the doctor, Pottegard suggested, because "hydrochlorothiazide is an effective and otherwise safe treatment for most patients".Besides treating hypertension, hydrochlorothiazide is frequently used for the treatment of congestive heart failure, symptomatic edema, diabetes insipidus and renal tubular acidosis. 

The pill is also used for the prevention of kidney stones in those who have high levels of calcium in their urine."Nevertheless, our results should lead to a reconsideration of the use of hydrochlorothiazide. Hopefully, with this study, we can contribute towards ensuring safer treatment of high blood pressure in the future," Pottegard noted.