The Physiomedical Dispensatory by William Cook, M.D., 1869
COW PARSNIP, MASTERWORT
Description: Natural Order, Umbelliferae. A large and strong-scented plant, four to eight feet high, perennial. Leaves once or twice ternately-compound; leaflets somewhat heart-shaped ; petioles broad and sheathing. Flowers white, small, in large flat umbels. Fruit obovate or orbicular, one-fourth to three-eighths of an inch long. Growing in damp and rich grounds.
Properties and Uses: The root of this plant is rank and acrid when fresh, but less acrid when dry. It is pronounced a strong antispasmodic, stimulant, and carminative, and has been reputed of much efficacy in hysteria, suppressed menstruation, colic, asthma, and even epilepsy. From personal experience, I can say nothing of the article; but the accounts of it lead me to suspect that it is an aero-narcotic poison. It is usually confounded with the angelica, which is the true masterwort; and it seems probable that the repute associated with heracleum, really belongs to the other article.
Medical Herbalism journal and medherb.com