Guaifenesin is an expectorant that helps reduce chest congestion caused by colds, infections or irritants. Proven to last up to 12 hours to provide powerful relief. Guaifenesin 600mg is an expectorant that helps reduce chest congestion caused by colds, infections or irritants. Compare to the active ingredient in Muci-nex. Our Phlegm relief pill is a unique bi-layer tablet that offers immediate relief via the first layer, and the second layers continues working for up to 12 hours. Thins and loosens mucus to alleviate chest congestion caused by excess phlegm, so you can go back to feeling like your normal self. Make your coughs more productive by helping loosen phlegm and thin bronchial secretions to rid the bronchial passageways of bothersome mucus and make coughs more productive. Safe for adults and children 12 years of age and older. Take 1 tablet with a full glass of water every 12 hours. Do not exceed 3 tablets over a 24 hour period.