Sildenafil is also used in both men and women to treat the symptoms of pulmonary arterial hypertension. When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. You can take this medicine with or without food 30 minutes before sex, depending on the dose. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Do not take a double dose to make up for a missed one. What side effects can this medication cause? If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. · Maximum dose: 20 mg orally three times a day. Injection: Initial dose: or 10 mg IV bolus three times a day. Comments: No greater efficacy was achieved with oral doses higher than the maximum recommended dose. A 10 mg injection dose is predicted to provide pharmacological effect equivalent to the 20 mg oral dose. 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. Even if this drug is covered by Medicare or your insurance, we recommend you compare prices. The MDRx coupon or cash price may be less than your co-pay. Brand Form .