Especially tell your healthcare provider if you take any of the following: medicines called nitrates medicines called guanylate cyclase stimulators such as Adempas riociguat medicines called alpha-blockers, such as Hytrin terazosin HCl , Flomax tamsulosin HCl , Cardura doxazosin mesylate , Minipress prazosin HCl , Uroxatral alfuzosin HCl , Jalyn dutasteride and tamsulosin HCl , or Rapaflo silodosin. Medicines that block an enzyme called CYP3A4. The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. A phone or video consultation is sometimes required for legal purposes. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure.Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. Viagra (sildenafil) and cost. Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile dysfunction. The cost of the drug with and without insurance can depend on several factors. Sildenafil Prices, Coupons and Patient Assistance Programs. Sildenafil is a member of the agents for pulmonary hypertension drug class and is commonly used for Erectile Dysfunction, Pulmonary Arterial Hypertension, and Sexual Dysfunction – SSRI Induced.. Brand names for sildenafil include Viagra, Revatio, and Liqrev. The cost for sildenafil .