The Asclepias tuberosa is a herbaceous, perennial plant, growing in most parts of the United States east of the Mississippi, and conspicuous in the summer by its large clusters of beautiful orange-red flowers. its root, which is the part used, is large, irregularly tuberous and branching, fleshy, externally brownish, internally white and striated. in the recent state it has a subacrid and nauseous taste, but when dried and powdered, is disagreeable only by its bitterness. Mr. E. Rhoads extracted from it a substance, which he believed to be its active principle. For the mode of preparing it, see the U. S. Dispensatory, 12th ed. it is yellowish, with the taste of the root, soluble in ether, and in less degree in water, from which it is precipitated by tannic acid.

In its influence on the system, asclepias appears to be diaphoretic and expectorant, in large doses often cathartic, and, according to some authorities, somewhat sedative to the circulation, while others consider it gently tonic. The chief therapeutic use which has been made of it, is in the treatment of catarrh, pleurisy, pneumonia, and phthisis; but it has been employed also in diarrhoea, dysentery, rheumatism acute and chronic, and for the promotion of the eruption in measles and other exanthematous fevers. The dose of the powder is from a scruple to a drachm, repeated every two or three hours till its effects are produced. As a diaphoretic it is better administered in the form of a decoction or infusion, made in the proportion of a troyounce to two pints, and given in teacupful doses, repeated as the powder.