More than one plant species is commonly referred to as a butterfly plant. One is butterfly bush, which refers to shrubs from the Buddleia genus. Butterfly weed (Asclepias tuberosa) is another. It is a type of milkweed that attracts butterflies.
The species most commonly referred to as butterfly bush, Buddleia davidii, is not poisonous to humans, according to the University of California Agriculture and Natural Resources. The ASPCA also reports that it is not toxic to animals. Buddleia asiatica, though, is poisonous.
Butterfly weed is poisonous to humans and animals. According to the U.S. Department of Agriculture, butterfly weed contains cardiac glycosides. Ingesting the plants can cause bloating, stupor, weakness, spasms, fever, breathing problems, pupil dilation and coma. It can cause problems standing or walking and a weak, rapid pulse. This plant is particularly important to Monarch butterflies, as they use butterfly weed and other milkweeds to lay eggs and feed larvae.
Common names, like butterfly plant, may be applied to different species of plants and may vary by region. Carefully check the species of your plant to ensure that it is nontoxic.