Mucinex® Expectorant Immediate/Extended-Release Tablets 600 mg guifenesin extended-release bi-layer tablets. Don't over medicate. If mucus is causing your congestion -- reach for Mucinex. This extended-release expectorant thins and loosens mucus, making coughs and nose-blowing more productive. Relieves Chest Congestion, Thins and loosens Mucus, 40 Bi-Layer Tablets.