Drug use Free Viagra is used to treat impotence in men. Viagra increases the body's ability to achieve and maintain erection during sexual stimulation. Viagra will not protect you from getting sexually transmitted diseases, including HIV. How Taken Generic Viagra comes as a tablet to take by mouth. Should be taken as needed about 1 hour before sexual activity. However, Viagra can be taken anytime from 4 hours to 30 minutes before sexual activity. Viagra should not be taken more than once a ...