"The tea comes from sweet wormwood (Artemisia annua), the Chinese plant that is a source for the world's most powerful anti-malarial treatments, which combine artemisinin derivatives with an older class of drugs. It can also be grown in wetter parts of Africa, and a year’s supply costs no more than a few dollars. Although the tea itself has traditionally been used in treatment, not prevention, in China, a randomized controlled trial on this farm showed that workers who drank it regularly reduced their risk of suffering from multiple episodes of malaria by one-third."
Full article: Wormwood tea to treat malaria: The WHO is opposed to an effective preventive medicine.