Mucinex is an expectorant medication containing 600 mg of guaifenesin in extended-release bi-layer tablets. Each pack contains 20 tablets designed to provide 12-hour relief from chest congestion by thinning and loosening mucus. The active ingredient guaifenesin helps break up chest congestion by thinning mucus, making it easier to clear airways. The extended-release bi-layer tablet technology provides sustained relief for up to 12 hours. This medication is intended to help relieve chest congestion associated with colds, infections, or allergies.