I have not used it, but here is some information for you:
Medicinal Uses: Used to relieve insomnia, anxiety and stress, as a diuretic in the treatment of rheumatism, arthritis and gout, as a remedy for chronic pain and for gastro-intestinal, kidney and bladder complaints. It is used as an intoxicating beverage which induces lethargy, drowsiness and dreams. (Stimulates, then depresses, the nervous system.)
Warning: Do not use when pregnant or breast-feeding or if suffering from depression. Do not use for longer than 3 months or in large doses without medical advice. Extended continuous intake can cause a temporary yellow discoloration of skin, hair and nails. Should never be taken with alcohol, barbiturates, anti depressants, antipsychotics, sedatives, sleeping pills, anaesthetics used during general anaesthesia. Can add to the effects of substances that depress the central nervous system, causing over sedation, even coma. It can also cause tremors, muscle spasms or abnormal movements that may decrease the effectiveness of anti-Parkinson's medications. These movement problems can also add to those caused by anti-psychotic medications. Increases the effects of CNS depressants and may lead to suicide. Possible side effects of Kava include gastrointestinal problems, liver problems, allergic skin reaction. Do not administer to persons under the age of 18.