Make sure you have discussed any other medications you are currently taking or plan to take before starting sildenafil with your doctor and pharmacist. Blood pressure may suddenly drop to life-threatening levels if Viagra Sildenafil is taken with any nitrate-containing medication e. These medicines are called PDE5 inhibitors. If this condition is not treated quickly, tissue damage and permanent loss of the ability to have an erection could result. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. Side effects Side effects of oral ED medicines are often mild. Sexual activity may be a strain on your heart, especially if you have heart disease.If you have these symptoms, stop taking VIAGRA and contact a doctor right away. have or have had heart problems such as a heart attack, irregular heartbeat, angina, chest pain, narrowing of the aortic valve, or heart failure. have low blood pressure, or high blood pressure that is not controlled. This means that 4 hours after you take a dose, your body has cleared half of the dose. In most cases, it takes about 5 half-lives for your body to completely remove a drug from your system. So. Welcome to provides prescription and OTC drugs through a leading pharmacy in Canada and other international .