If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. Sildenafil does not prevent pregnancy or the spread of sexually transmitted diseases such as the human immunodeficiency virus (HIV). If you are taking sildenafil to treat erectile dysfunction, follow your doctor's instructions and the guidelines in this paragraph. Take sildenafil as needed before sexual activity. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time between 4 hours and 30 minutes before sexual activity. Sildenafil citrate 100 mg Price should not usually be taken more than once every 24 hours. If you have certain health conditions or are taking certain medications, your doctor may direct you to take sildenafil less often. You can take sildenafil with or without food. However, if you take sildenafil with a high-fat meal, it will take longer for the medicine to work. If you are taking sildenafil to treat PAH, follow your doctor's instructions and the guidelines in this paragraph. You will probably take sildenafil three times a day with or without food. Take sildenafil at around the same time every day, and space your doses 4 to 6 hours apart.