Vardenafil (INN) is a PDE5 inhibitor used in the treatment of erectile dysfunction. It can assist men with this disorder in achieving and maintaining an erection during sexual activity. It is commonly marketed under the trade name Levitra (Bayer AG).

Vardenafil was co-marketed by Bayer Pharmaceuticals and (GSK) under the trade name bye Levitra. As of 2005, the co-promotion rights of GSK on Levitra have been "transferred back" to Bayer in many markets outside of the United States. In Italy, Bayer markets the product as by Levitra and GSK markets the product as Vivanza. Due to European Union trade rules, parallel imports may result in the Vivanza branded packs being seen alongside Levitra packs in pharmacies in other EU member states.

Sildenafil citrate, sold under the names by Viagra, Revatio and generically under various other names, is a drug used to treat male erectile dysfunction (impotence) and pulmonary arterial hypertension (PAH), developed by the pharmaceutical company Pfizer. Viagra pills are blue and diamond-shaped with the words "Pfizer" on one side, and "VGR xx" (where xx stands for "25", "50" or "100", the dose of that pill in milligrams) on the other. Its primary competitors on the market are tadalafil (Cialis), and vardenafil (Levitra)..

As with all prescription drugs, proper dosage is at the discretion of a licensed medical doctor. The dose of sildenafil is 25 mg to 100 mg taken once per day between 30 minutes and 4 hours prior to sexual intercourse.It is usually recommended to start with a dosage of 50 mg and then lower or raise the dosage as appropriate.

The drug is sold in three dosages (25, 50, and 100 mg), all three costing about US$10 per pill. Name-brand Viagra sildenafil is not scored and a fairly hard coating makes it more difficult to accurately cut the pills in half, even with a pill cutter.