As erectile dysfunction has been linked with an inadequate blood flow to the penis, causing the inability to obtain or maintain an erection that is deemed suitable for penetrative sex, the active ingredient Sildenafil Citrate has been found to increase the flow of blood through the body. How Do I Take Viagra? Key facts It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. One a penny, two a penny It can be dangerous to take sildenafil if you also take medicines called nitrates often given for chest pain. This medicine is available on prescription and you can also buy it from most pharmacies.Viagra is a well-known, branded and common erectile dysfunction (ED) treatment for men. It’s available on prescription through our Online Doctor service. The original brand that’s . Erectile dysfunction tablets like Viagra can help you get and keep an erection. We’re a service that helps you order treatments online from UK-registered doctors with free, . 16 tablets. ? / month. ? One-time or subscription. Viagra for men, often referred to as the ‘blue pill’, is an ED pill which can help to improve sexual wellbeing by enhancing .