Sildenafil citrate is the active ingredient in cenforce d tablet. Which is used to treat the problem of erectile dysfunction which is always seen in men. The effect of this drug lasts for 4 to 6 hours. And if the effect of this medicine is more than that, seek the help of a doctor immediately. Do not do heavy work like driving and operating machinery after taking this medicine as common side effects like dizziness are seen after taking this medicine.