Guaifenesin 1200 mg Extended Release Tablets, 14 ct, QC99706 Sale! This item is currently on backorder but you can still purchase it now and we'll ship as soon as more become available. Compare to the Active Ingredients in Mucinex Maximum Strength. Helps loosen phlegm (mucus) and thin bronchial secretions to rid the bronchial passageways of bothersome mucus and make coughs more productive. 12-hour relief.