Milkweeds were deemed medicinally active plants from early times and consequently appeared in pharmacopoeias. Additionally, several glycosides and a small amount of an alkaloid have been isolated. All species of Asclepias and distasteful to livestock. Still, severe losses have occurred, especially in sheep, but only when the animals were forced to eat milkweeds because of over-grazing or drought. Tetanic seizures occurring repeatedly at short intervals are common.
Death usually follows a comatose period of variable duration.
Bloodflower milkweed contains cardiac glycosides, which affect vertebrate heartbeat, so is toxic to birds and mammals. Such butterflies are distasteful to insect-eating birds, suggesting that danaid butterflies have biochemical mechanisms for eating milkweeds containing the toxin, and storing this poison in their tissues. When the butterflies feed on other milkweed species they are nontoxic. Bigelow, J. 1814. Cummings, Hilliard and Co., Boston.