Fildena is typically taken orally with water, about 30 minutes to 1 hour before anticipated sexual activity. Sexual stimulation is necessary for the medication to work effectively. The effects of Fildena can last for about 4 to 6 hours, providing a window of opportunity for sexual activity. Common side effects of sildenafil medications, including Fildena, may include headache, flushing, indigestion, blurred vision, and nasal congestion.