Only Mucinex 12-Hour Chest Congestion Expectorant Tablets has an extended release bi-layer tablet to deliver congestion relief. The first layer is absorbed quickly by your body for fast-acting relief. The other layer dissolves slowly to continue relieving your chest congestion for 12 hours. Mucinex 12-Hour Chest Congestion Expectorant Tablets Relieves Chest Congestion, Thins and loosens mucus. Mucinex contains active ingredient 600 mg Guaifenesin.