The present invention provides plant extracts, isolated alkaloids, synthetic alkaloids and compositions having antitussive activity. In some preferred embodiments, the plant extracts and the isolated alkaloids are from a plant of a genus in the family Stemonaceae. In other preferred embodiments, the plant extracts and the isolated alkaloids are from a plant of the genus Stemona, Croomia, or Stichoneuron. In especially preferred embodiments, the plant extracts and the isolated alkaloids are from the plant Stemona tuberosa. The present invention further provides methods for isolating such plant extracts and alkaloids. In addition, the present invention provides methods for reducing or suppressing coughing by administering plant extracts, alkaloids and compositions having antitussive activity.