Value Size. 600mg Guaifenesin Extended-Release Bi-Layer Tablets. May Temporarily Relieve Chest Congestion. Thins and Loosens Mucus. Immediate and Extended Release. When youre sick, mucus can be a master of mayhem. But quick, long-lasting chest congestion relief is just a dose away with Mucinex extended-release bi-layer tablets that start to work fast and last for 12 hours. May Temporarily Relieve chest congestion caused by excess Mucus. Thins & loosens mucus. Starts to work right away & lasts for 12 hours. Extended Release Bi-Layer Tablets. Mucinex is the #1 doctor recommended OTC expectorant among Internists, General Practitioners & Family Practitioners