Tadalafil is a drug used to treat male erectile dysfunction (impotence). It was developed by the biotechnology firm ICOS and marketed worldwide by Eli Lilly and Company under the brand name Cialis. It works by inhibiting an enzyme known as PDE5. Due to its 36-hour effect it is also known as the "Weekend Pill". In the United States, tadalafil has Food and Drug Administration approval and became available in December, 2003.

Tadalafil is in a class of medications known as PDE-5 inhibitors, which are used to treat cases of male impotence. Elli Lilly and Icos are currently marketing Tadalafil in the U.S., UK, EU , and countries around the world.

Tadalafil acts in the same way as Sildenafil (Viagra), by blocking an enzyme called phosphodiesterase-5, or PDE-5. Tadalafil is more targeted than Sildenafil which results in fewer sides effects and lower dosage. Tadalafil helps the smooth muscles in the penis relax and widen, which allows for more blood to enter. As a result, you gain erections faster and easier with Tadalafil.

Tadalafil is approved in authorized markets for the treatment of mild to severe ED at both 10 and 20 mg Tadalafil doses. When you buy Tadalafil, the labels in each of these markets indicate that the product should be taken prior to anticipated sexual activity and without regard to food. Just like Sildenafil, sexual stimulation is needed for Tadalafil to work.