Taking sildenafil alone will not cause an erection. What special dietary instructions should I follow? Do not use more of it and do not use it more often than your doctor ordered. Your doctor may need to change the doses of your medications or monitor you carefully for side effects. If you prefer, you may contact the U.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 .  · VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. 4. Contraindications. Rarely reported side effects include: an erection that will not go away (priapism). If you have an erection that lasts more than 4 hours, get medical help right away. If it is not treated right away, priapism can permanently damage your penis. sudden vision loss in one or both eyes.