If you have COPD or cystic fibrosis, you may be taking a prescription expectorant, or your doctor may have suggested an over-the-counter expectorant, such as Mucinex® (Guaifenesin). But did your doctor explain the expectorant's purpose to you? What does an expectorant do and how does it help you breathe easier? Learn about expectorants and how they help to clear the airways and allow for better breathing.