Commonly prescribed blood pressure medications can sensitize the skin to ultraviolet radiation from the sun. The diuretic hydrochlorothiazide or HCTZ is found in dozens of blood pressure pills. A new study suggests that this drug as well as another antihypertensive medication called nifedipine may increase the risk of lip cancer. Such photosensitizing drugs absorb ultraviolet energy and increase the likelihood of cellular damage. Previous research has shown that these medications may predispose people to squamous cell skin cancer. People taking diuretics like hydrochlorothiazide should be especially careful to protect their skin and lips from ultraviolet sun exposure.