Its effects often last for 4 to 5 hours. Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension. Patients should always ask their doctors for medical advice about adverse events. Medicines that you take by mouth are called oral medicines. Medical consultations were also taken into consideration, as PDE5 inhibitors require a valid prescription from a licensed medical provider. This information is reviewed by a licensed practitioner who will assess your eligibility for the medication.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Drug Images What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. . Viagra. Compare prices and print coupons for Sildenafil (Generic Revatio and Viagra) and other drugs at CVS, Walgreens, and other pharmacies. Prices start at $