It works for up to 36 hours. Side effects Side effects of oral ED medicines are often mild. Your medical provider will adjust your dose if necessary. These are commonly prescribed for an enlarged prostate or male pattern baldness. Children 1 year of age and older weighing 45 kilograms kg or more—20 mg 3 times a day. 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. You need a prescription from a doctor to obtain sildenafil.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 test1.ru drug is more popular than comparable drugs. It is available in generic and brand versions. Generic sildenafil is covered by most Medicare and insurance plans, but . Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work.  · Do not take VIAGRA if you take medicines called guanylate cyclase stimulators which include: Tell all your healthcare providers that you take VIAGRA. If you need emergency medical care for a heart problem, it will be important for your healthcare provider to know when you last took VIAGRA. ID/FEI Business Operations; Pfizer.