Sildenafil is taken by mouth as needed, at least 30 minutes, but no more than 4 hours, before sexual activity (1 hour before is the most effective). Do not take more often than once daily, and take as directed. A high fat meal may delay the time of onset of this drug. Avoid eating grapefruit or drinking grapefruit juice while you are being treated with this medication unless your doctor instructs you otherwise. The dosage is based on your medical condition, response to therapy, and other medications you may be taking (see also Drug Interactions section).