in medicine, the dried bark of the black haw or Viburnum prunifolium, grown in India and North America. The black haw contains viburnin and valerianic, tannic, gallic citric and malic acids. The British Pharmacopoeial preparation is the Extractum Viburni Prunifolii liquidum; the United States preparation is the fluid extract prepared from the Viburnum opulus. The physiological action of viburnum is. to lower the blood pressure. In overdose it depresses the motor functions of the spinal cord and so produces loss of reflex and paralysis. Therapeutically the drug is used as an antispasmodic in dysmenorrhoea and in menorrhagia.