Argemone mexicana (Mexican Poppy, Mexican Prickly Poppy or Cardosanto) is a species of poppy found in Mexico and now widely naturalized in the United States, India and Ethiopia. An annual herb with bright yellow sap, it has been used by the Natives of the western US and parts of Mexico. The seed-pods secrete a pale-yellow latex substance when cut open. This argemone resin contains berberine and protopine, and is used medicinally as a sedative.
The seeds contain 22–36% of a pale yellow non-edible oil, called argemone oil or katkar oil, which contains the toxic alkaloids sanguinarine and dihydrosanguinarine. Surprisingly, the oil is used to grease the cooking plate to bake the injera in Ethiopia. The seeds resemble the seeds of Brassica nigra (mustard). As a result, mustard can be adulterated by argemone seeds, rendering it poisonous. The oil itself is used medicinally to treat dropsy, jaundice and skin diseases. Katkar oil poisoning causes epidemic dropsy, with symptoms including extreme swelling, particularly of the legs. Several significant instances of katkar poisoning have been reported in India, Fiji, South Africa and other countries. The last major outbreak in India occurred in 1998. 1% adulteration of mustard oil by argemone oil has been shown to cause clinical disease.