Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. The effects may be increased because of slower removal of the medicine from the body. Do not use more of it and do not use it more often than your doctor ordered. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine. To provide you with the most relevant and helpful information, and understand which information is beneficial, we may combine your email and site usage information with other information we have about you. 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.Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may. For oral dosage form (tablets): Adults up to 65 years of age—50 milligrams (mg) as a single dose no more than once a day, 1 hour before sexual intercourse. Alternatively, the medicine may be taken 30 minutes to 4 hours before sexual intercourse. Both Viagra and sildenafil are available in mg, mg, and mg doses. REX MD currently has a out of 5-star rating on Trustpilot as of November About 84% of the over 3, reviews.