Cialis is a medication used to treat erectile dysfunction (ED) and benign prostatic hyperplasia (BPH). Its active ingredient is Tadalafil, a type of phosphodiesterase type 5 (PDE5) inhibitor. Cialis helps increase blood flow to the penis during sexual stimulation, making it easier to achieve and maintain an erection. For men with BPH, it can help relax the muscles in the prostate and bladder, easing urinary symptoms.