Cialis, known generically as tadalafil, is a medication primarily used to treat erectile dysfunction (ED) and symptoms of benign prostatic hyperplasia (BPH). It works by relaxing the muscles of the blood vessels, increasing blood flow to particular areas of the body. This action helps maintain an erection following sexual stimulation and can also relieve symptoms of BPH such as difficulty in beginning the flow of urine, weak stream, and the need to urinate frequently or urgently (including during the middle of the night). Cialis is known for its long-lasting effect, which can remain in the body for up to 36 hours, providing flexibility in sexual activity.