Cialis is a brand-name prescription medication. Tadalafil may not be safe for people with certain medical conditions, including people who have had a stroke , have coronary heart disease or retinitis pigmentosa an eye disease. ED occurs more frequently in older men. When will Cialis be available to pharmacies? Combined use could lead to additional lowering of blood pressure, possibly to unsafe levels. · Cialis is a prescription drug used to treat erectile dysfunction and benign prostatic hyperplasia. Learn about its dosages, form, strengths, and more. Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) . The most commonly reported side effects in patients treated with Cialis during the testing of the product were: headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who.