Mucinex DM gets mucus out. Fight congestion caused by flu, colds and coughs with Mucinex DM 12-hour maximum-strength tablets. Adults take one tablet and it helps thin and loosen mucus, relieving chest congestion and controlling coughs. Mucinex DM is designed with bi-layers for 12 hours of extended-release relief. This box contains 20 tablets. Each tablet has 600 mg. of guaifenesin and 30 mg. of dextromethorphan HBr.