Guaifenesin & Levomenthol. Aids a productive cough. Thins and loosens chest mucus. REDUCES CHEST CONGESTION. When you're suffering from a deep, chesty cough, but still want to get on with your normal daily routine, Benylin Mucus Cough works deep down to loosen phlegm, clear bronchial congestion, and make your cough more productive. Non-Drowsy Formulation.