It works for up to 36 hours. You can see if Viagra is a good choice for your ED by speaking with a doctor locally or online with our secure telemedicine platform. An inherited eye disease that affects the retina. Published June 25, Because it improves blood flow to the penis, Viagra sildenafil citrate treats erectile dysfunction ED effectively. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. · It is not recommended to take Viagra without a prescription as it can cause harmful side effects and potentially hazardous interactions, especially when mixed with . Still, if your doctor says it’s okay for you to use and you end up paying out-of-pocket, you can still get the generic for a lot less than Viagra. According to price . 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 .