Place the tip of the syringe into you or your child’s mouth and point it towards the cheek. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. Remove the syringe from the bottle. This boosts blood flow and helps you get an erection from sexual activity. These are commonly prescribed for an enlarged prostate or male pattern baldness. What special precautions should I follow? Sildenafil usually should not be taken more than once every 24 hours.Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels. Viagra is available in three strengths: 25 milligrams (mg), 50 mg, and mg. Note: Sex and gender exist on spectrums. Use of the term “male” in this article refers to sex assigned at birth.