Kava (Piper methysticum). Neiafu, Vava'u, Tonga. The Kava plant has been used for centuries as a ceremonial beverage in South Pacific Island cultures. Its numbing properties have led to its use as an herbal remedy to treat a variety of medical conditions. An extract from the root of the plant is used to make a cola beverage which is said to have a relaxing, calming effect.