Medicines that block an enzyme called CYP3A4. Slowly pull back the plunger until the required dose. What special precautions should I follow? This includes prescription or nonprescription over-the-counter [OTC] medicines and herbal or vitamin supplements. Use only the brand of this medicine that your doctor prescribed.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 carrying blood to the lungs, causing shortness of breath, dizziness, and tiredness). What to consider Cost Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription.  · Products and services Proper Use Drug information provided by: Merative, Micromedex ® Use sildenafil exactly as directed by your doctor. Do not use more of it and do not use it more often than your doctor ordered. If too much is used, the chance of side effects is increased. This medicine comes with a patient information leaflet.