Viagra is an oral drug for male impotence, also known as erectile dysfunction.

Having been around for a lot longer, Viagra has a great safety track record and proven effects that start acting in 30 minutes and last for about 5 hours.

Cialis is used for treating erectile dysfunction in men (e.g., impotence).

Comparing with Viagra, Cialis works in as quickly as 30 minutes and lasts for about 36 hours while Viagra effect lasts up to 5 hours.