How much does my medication cost? Search for and select the medication you were prescribed. Cialis tadalafil : This ED medication works with the same principle as Viagra, but lasts up to 36 hours. Other warning signs of an unsafe online pharmacy include outdated medication, no customer service, or suspiciously low prices. You take one 2.Sildenafil oral tablet is available as the brand-name drugs Viagra and Revatio. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name . Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 .