· Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be .Storage Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. It is completely safe to take Viagra or Sildenafil provided you are male and over, and have been prescribed it for erectile dysfunction. Keep from freezing. Click here for an email preview. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. · Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Do not take two doses at . Viagra works at its best within a few hours after it’s taken. In most people, the drug is most effective about 1 hour after it’s taken. Over time, Viagra is slowly .  · Adults 65 years of age and older—25 mg as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be .Viagra contains the active ingredient Sildenafil, which is also available in an unbranded generic form. Avoiding antacids: Eating a light meal will help out with this one! If we combine this information with your protected health information, we will treat all of that information as protected health information and will only use or disclose that information as set forth in our notice of privacy practices. The following information includes only the average doses of this medicine. Side effects are uncommon and generally mild, if you experience any serious pain or side effects which last longer than hours, seek medical attention immediately. When side effects do occur , these are generally mild and short-lived. Most commonly you might experience some flushing, stomach ache or indigestion, or a headache.