Taking Cialis does not mean you are guaranteed to get an erection. The medication will be effective for up to 36 hours. For further information contact your pharmacist or Eli Lilly and Company directly. There may be rare occurrences of priapism or painful, prolonged erections. You need a prescription from a doctor to buy tadalafil.Cialis comes in several strengths: milligrams (mg), 5mg, 10 mg, and 20 mg. The Cialis cost per pill and daily cost depend on several factors, such as: the strength prescribed by your doctor. Tadalafil (Cialis) is a phosphodiesterase-5 enzyme (PDE-5) inhibitor. It works by blocking PDE This is a protein in your body that breaks down the molecules that normally cause an erection. When it blocks PDE-5, tadalafil (Cialis) helps an erection occur by allowing certain muscles in the penis to relax and the penis to fill with blood. We have good news for you: generic Cialis, used to treat erectile dysfunction (ED)and enlarged prostates, just hit pharmacies. Prices for the generic, known as tadalafil, are more than 50% less than those of brand-name Cialis. As more men are able to afford tadalafil and treat their ED, it’s likely that many will have questions.