Its effects often last for 4 to 5 hours. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. Also tell your doctor if you or any of your family members have or have ever had an eye disease such as retinitis pigmentosa an inherited eye condition that causes loss of vision or if you have ever had sudden severe vision loss, especially if you were told that the vision loss was caused by a blockage of blood flow to the nerves that help you see. Do not start these medications while taking sildenafil without discussing it with your healthcare provider. All of which require time to take effect.4 min read If it’s temporary and only happens occasionally, problems getting or keeping an erection aren’t cause for concern. There could be any number of reasons. It could be . Overdose Ask your doctor Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription . Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects .
