A white or yellowish white crystalline substance, C20H14O4, formed by condensation of the anhydride of phthalic acid and phenol. Its solution in alkalies is brilliant red, but is decolorized by acids. This reaction, being very delicate, is used as an indicator. It is sometimes used as a laxative in veterinary medicine.

An organic compound used as an acid-base indicator. The compound is colorless in acidic solution and pink in basic solution (with the transition occuring around pH 8.3). Phenolpthalein was used for many years as a laxative in very low concentrations- high concentrations are toxic

a laxative used in many preparations under various trade names; also used as an acid-base indicator in titrations involving weak acids and strong bases because it is brilliant red at high alkalinity and colorless below pH 8