Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. Alpha-blockers are sometimes prescribed for prostate problems or high blood pressure. John’s wort. However, the dose is usually not more than 80 mg 3 times a day. Remove the syringe from the bottle. Proper Use Use sildenafil exactly as directed by your doctor. If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire.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 carrying blood to the . Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is mg. Don’t take sildenafil (Viagra) more than once daily (at any dose). Written by Brian Leonard, PharmD, BCACP, BCGP.  · Viagra is used as needed, meaning you only take a dose prior to sexual activity. Cialis can be prescribed for use as needed, but can also be prescribed for use once per day, every day (without.