Blue Vervain [Nervous], sometimes called wild hyssop or traveler's joy, dates back to at least since the Middle Ages. It is considered a bitter and a tonic by herbalists, who use the plant's leaves and flowers. The plant contains glycosides, volatile oil, tannin, alkaloids and bitter substances. Nature's Sunshine offers blue vervain in a highly concentrated liquid form. The active substances are extracted and suspended in a base of pure vegetable glycerin. This liquid extract contains no preservatives or additives. Take 1/2 to 1 teaspoon three times daily. Children take one-half the adult dose.