Grapefruit may interact with tadalafil and lead to unwanted side effects. Use Cialis Tadalafil exactly as directed on the label, or as prescribed by your doctor. Use the medicine exactly as directed. Take Cialis just before sexual activity, but not more than once per day. You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail. Dosing The dose of this medicine will be different for different patients. Take the medicine at the same time each day, with or without food. · 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.  · 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 .