From Everything.Sucks

Tadalafil, sold under the brand name Cialis among others, is a medication used to treat erectile dysfunction (ED), benign prostatic hyperplasia (BPH), and pulmonary arterial hypertension. It is a tablet taken by mouth. Onset is typically within half an hour and the duration is up to 36 hours.Common side effects include headache, muscle pain, flushed skin, and nausea. Caution is advised in those with cardiovascular disease.

A user shared in a review "I have been taking 5mg Cialis daily for 6 weeks and have not had an erection at all. Only leg cramps and pain."