You may attempt sexual activity at any time between doses. Click here for an email preview. For this purpose, one dose works for up to 72 hours. Sexual activity may be a strain on your heart, especially if you have heart disease. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV.Cialis takes from 30 minutes to 2 hours to take effect. It can last up to 36 hours. Cialis is a PDE5 inhibitor medication approved for use for erectile dysfunction (ED) and benign prostatic. Cialis; Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called . Erectile dysfunction medications, including Viagra and Cialis, help the muscles in the penis relax so you can get and maintain an erection. But these drugs differ by side effects, dosage schedule.