Benylin Mucus Cough Max Honey & Lemon helps to relieve chesty (productive) coughs by thinning and loosening chest mucus (phlegm), making it easier to cough up. The maximum strength formula reduces chest congestion. Mucus coughs are caused by a build-up of mucus in the lungs and on the chest. The cough mechanism kicks in to try and get rid of this excess mucus. Active ingredient guaifenesin helps to thin and loosen mucus in your chest, making it easier to cough up. Please note that results may vary.