The whole herb is used, the drug consisting of both the fresh and the dried herb. The tops of the young shoots contain the greatest virtues of any part of the plant. The shoots are gathered before the plant flowers. The volatile oil is contained in glands distributed over the whole plant and contains caprinic, plagonic, caprylic and oenanthylic acids - also a yellow crystalline body, called rutin. Oil of Rue is distilled from the fresh herb.
Water serves to extract the virtues of the plant better than spirits of wine.
Decoctions and infusions are usually made from the fresh plant, or the oil may be given in a dose of from 1 to 5 drops. It is used, powdered, for making tea. In excessive doses, it is an acro-narcotic poison, and on account of its emetic tendencies should not be administered immediately after eating. It forms a useful medicine in hysterical affections, in coughs, croupy affections, colic and flatulence, being a mild stomachic. The oil may be given on sugar, or in hot water.