Cialis 5mg tablets are a prescription medication used to treat erectile dysfunction (ED) In men. Cialis 5mg (Tadalafil) tablets are taken by mouth once a day, with or without food. The medication can be taken at any time of day, but it is important to take it at the same time each day. (Tadalafil) Cialis works by increasing blood flow to the penis, which makes it easier to get and keep an erection. It also relaxes the muscles in the prostate gland, making it easier to urinate.