For treatment of erectile dysfunction: For oral dosage form tablets : Adults up to 65 years of age—50 milligrams mg as a single dose no more than once a day, 1 hour before sexual intercourse. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive. Sildenafil may cause side effects. The body takes longer to absorb it after a high-fat meal or alcohol. Some medications should not be taken with sildenafil.Sildenafil is used to treat erectile dysfunction (ED) and to reduce blood pressure in pulmonary arterial hypertension (PAH). It is taken when needed for ED and daily for PAH. A headache, stomach upsets, and flushing are the main side effects, and it should not be taken within 24 hours of a nitrate. 5. Tips. Prices at Rite Aid Pharmacy for Popular Prescriptions. Drug Name. Lowest GoodRx Price. tadalafil (Cialis) (Generic Cialis) 30 tablets 5mg. $ with free Coupon. Get Free . Sildenafil oral tablet is a prescription medication used to treat erectile dysfunction (ED) and pulmonary arterial hypertension (PAH). mg once per day. Child dosage (ages 0–17 years).