Tadalafil is also used to treat men who have signs and symptoms of benign prostatic hyperplasia BPH. BPH is caused by an enlarged prostate. You may take this medicine with or without food. Tadalafil is in a class of medications called phosphodiesterase PDE inhibitors. Read it again each time you refill your prescription in case there is new information. Tadalafil, its supposed active ingredient, can cause eye redness, headaches, and facial flushing.AdSave on 50, Brand Name & Generic Drugs With SingleCare®. Get Your Free Rx Coupon Now! Find the Lowest Price for Your Prescription and Save at Your Local Pharmacy : Maintenance, Accute, Branded, Generic.  · Adults—5 milligrams (mg) once a day, taken at the same time each day, without regard for the timing of sexual activity. Children—Use is not recommended. For treatment of pulmonary arterial hypertension: Adults—40 milligrams (mg) (two 20 mg tablets) taken once a day. Take both tablets at the same time each day. Do not divide . Generic: Tadalafil. Form: oral tablet; Strengths: mg, 5 mg, 10 mg, and 20 mg; Brand: Cialis. When to take your dose: Take one tadalafil tablet before you expect to have sexual activity.