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. Your doctor may adjust your dose as needed and tolerated. The following information includes only the average doses of this medicine. Do not take a double dose to make up for a missed one. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand.1. Avoid taking Viagra with a large meal or high-fat meal. Viagra blood levels peak an hour after you swallow the tablet on an empty stomach. According to Ramin, if you eat a large or high-fat. 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.