Sildenafil usually needs to be taken 24 hours apart to be able to take a 2nd dose. Sildenafil works on the male reproductive system and can be used to treat erectile dysfunction disorders of the penis. Sildenafil can be taken up to once a day, and the drug can be useful during sexual stimulation. Patients can specify the exact time for the 2nd dose of the drug according to their situation, usually a minimum interval of 24 hours is required. Sildenafil may also cause headaches, dizziness, facial edema and allergic reactions. Patients should take sildenafil under the guidance of a doctor, rational use of medication, to prevent adverse effects on the body.