Viagra 100mg Tablet may be taken on an empty stomach or with a meal. It should be strictly taken as advised by your doctor. You should take about 1 hour before you plan to have sex. The amount of time it takes to work varies from person to person, but it normally takes between 30 minutes and 1 hour. This medicine will only help you to get an erection if you are sexually stimulated. However, you should not take this medicine if you do not have erectile dysfunction. It should not be taken more than once a day.