How to Use Viagra 100mg Tablet? Viagra 100mg Tablet (Sildenafil)can be taken 30-60 minutes before engaging in sexual activity. However, you may also take it up to 4 hours prior to sex. Furthermore, this medicine will assist you in achieving and maintaining an erection only if you are sexually stimulated. It is important to note that you should not take extra pills in an attempt to achieve quicker results. Additionally, as Sildenafil is specifically formulated for the treatment of erectile dysfunction, it is intended solely for men; therefore, it is not recommended for use by women or children.