A pharmaceutical composition contains a therapeutically effective amount of an active ingredient, in admixture with a pharmaceutically acceptable carrier or diluent for the active ingredient, in which the active ingredient is i) a polar solvent extract of Polygala, the polar solvent being water or a mixture of water and methanol or ethanol; ii) an aqueous fraction resulting from an extraction of the polar solvent extract with an organic solvent; iii) an organic eluate by introducing the polar solvent extract or the aqueous fraction into a reverse phase chromatography column, and eluting the column with water and an organic solvent; or iv) a filtrate having a molecular mass less than 30000 in the organic eluate.