Follow your doctor’s directions carefully, and ask your doctor or pharmacist to explain any part you do not understand. Tadalafil is sometimes taken as needed, usually at least 30 minutes before sexual activity and not more often than once every 24 hours. If you are taking tadalafil on a regular schedule, take it at around the same time every day. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately or get emergency medical treatment, and avoid sexual activity until your doctor tells you otherwise.Brand-name Cialis: $20 – $80 per dose (5mg, 10mg, 20mg) Generic Cialis (tadalafil): $11 – $44 per dose (5mg, 10mg, 20mg) Daily generic Cialis (tadalafil): $8 per . The most commonly reported side effects in patients treated with Cialis during the testing of the product were: headache. indigestion. back pain. muscle pain. flushing. stuffy nose. Patients who. Tadalafil is a medicine used to treat erectile dysfunction (ED, also called impotence) and problems with urination caused by an enlarged prostate (benign prostatic hypertrophy or BPH). It is sometimes known by its generic name tadalafil, and sometimes known by its trade name, Cialis. There are also other brands of this medicine available.