What it does: Benylin® Mucus Cough Max Honey & Lemon Flavour Syrup works to thin and loosen mucus making it easier to cough up. How it works: Active ingredient guaifenesin helps to thin and loosen mucus in your chest, making it easier to cough up. What is a mucus cough? When mucus builds up in the chest, it can be hard to get rid of by coughing, so it’s helpful to have something to take to loosen the mucus and relieve the feeling of heaviness.