Mucinex Maximum Strength 12-Hour Chest Congestion Medicine Expectorant Tablets! Only Mucinex has an extended release bi-layer tablet to deliver maximum-strength 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 Maximum Strength contains 1200 mg of Guaifenesin bi-layer tablets and helps relieve chest congestion alone with thinning and loosening mucus.