Take the medicine at the same time each day, with or without food. The amount of medicine that you take depends on the strength of the medicine. Keep from freezing. Common side effects may include: headache; flushing warmth, redness, or tingly feeling ; nausea, upset stomach; runny or stuffy nose; or muscle pain, back pain, pain in your arms, legs, or back. If your dose is different, do not change it unless your doctor tells you to do so. Avoid the use of grapefruit products. Tadalafil works for these conditions by promoting muscle relaxation, which improves blood flow in PAH and urinary flow in BPH. · Cialis (tadalafil) is prescribed to treat erectile dysfunction and symptoms of benign prostatic hyperplasia. It comes as a tablet that’s taken as needed or once per . Generic Cialis (tadalafil): starting at $40 per month (5mg, 10mg, 20mg) Daily generic Cialis (tadalafil): starting at $40 per month (mg, 5mg) Product details. Dosage for erectile dysfunction (ED) For treating erectile dysfunction (ED), Cialis may be used daily or on occasion. Cialis ED dosage for daily use For treating ED, .