This medication is taken with or without food an hour before sex. If we combine this information with your protected health information, we will treat all of that information as protected health information and will only use or disclose that information as set forth in our notice of privacy practices. How and when to take sildenafil It’s important to take sildenafil as advised by a doctor or pharmacist. If your dose is different, do not change it unless your doctor tells you to do so. If you see air bubbles in the syringe, repeat the steps. If you often forget doses, it may help to set an alarm to remind you.If you are experiencing symptoms of ED and are considering a generic version of Viagra, your doctor can prescribe a generic alternative to ensure it is safe and FDA-approved. 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 . You can take Viagra take 30 minutes to 4 hours before sexual activity, but it shouldn’t be taken more than once daily. For most men, Viagra begins to work within an hour. Viagra .