SILDENAFIL treats erectile dysfunction (ED). It works by increasing blood flow to the penis, which helps to maintain an erection. Take this medication by mouth with a glass of water. Follow the directions on the prescription label. The dose is usually taken 1 hour before sexual activity. You should not take the dose more than once per day. Do not take your medication more often than directed. Talk to your care team about the use of this medication in children. This medication is not used in children for this condition.