Kava Kava Root (Piper methysticum). Kava Kava, as an analgesic sedative is used to relieve pain in rheumatism, alleviate insomnia and calm anxiety. Kava Kava root is also known as one of the most powerful of the herbal muscle relaxants. It is helpful in increasing flexibility influencing the motor units of the nervous system, relaxing muscle tension and aiding with structural alignments. Being a potent analgesic, it can be applied directly to a painful wound or taken internally.