The active ingredient in filagra, sildenafil citrate, works to activate sexual arousal. It is most effective if taken one hour before sexual activity. The effectiveness of one dose lasts for 4-5 hours and should be taken once a day. It is imperative to consult a doctor before taking this medicine. Buy this drug at a cheap price on eretilepharma.com. It is necessary to take a doctor's advice before using this medicine.