Foster & Thrive Tussin expectorant helps loosen phlegm (mucus) and thin bronchial secretions to make coughs more productive.. There are 200 milligrams of guaifenesin per 5 mL dose.. Compare to active ingredient in Robitussin® Mucus + Chest – a registered trademark of Haleon.. 4-ounce bottle of adult formula is suitable for anyone age 12 or older..