How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Take sildenafil as needed before sexual activity. You can take sildenafil with or without food. Click here for an email preview. Severe liver disease. Summary Cialis and Viagra are both pills for treating erectile dysfunction. Vardenafil usually works for 4 to 5 hours.Typical dosing for Sildenafil (Viagra) The typical dose is to take 50 mg of sildenafil (Viagra) by mouth, about 1 hour before sex, as needed. The maximum recommended dose is . Price without insurance: starts at $6 per dose for 10 doses. Doses: 20, 25, 50, and mg. Supply: 30, 90, or days. Sildenafil is the generic form of Viagra and Revatio. It’s chemically. 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.