BENYLIN® Mucus Cough Max Menthol works on your chest mucus, helping to thin it out and making it easier to cough up. It also has the invigorating taste of menthol. Maximum strength formula Deep penetrating relief Soothes your cough fast Menthol flavour How BENYLIN® Mucus Cough Max Menthol works: Guaifenesin gets to work in BENYLIN® Mucus Cough Max Menthol, helping to thin and loosen mucus in your chest. Guaifenesin is an expectorant, which means it makes mucus easier to cough up, helping to relieve chest congestion.