You can take this medicine with or without food 30 minutes before sex, depending on the dose. Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. Here’s some information to help you get ready and know what to expect from your doctor. Some people may also have ringing in their ears tinnitus or dizziness. This site is intended only for U. How should this medicine be used?Viagra vs. over-the-counter products. Many over-the-counter (OTC) products may be advertised to help with ED. Examples of these products include: . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. . In fact, a recent review of studies found that some counterfeit drugs contained a very high, dangerous level of sildenafil that far exceeded a typical .