Kava comes from the root of a shrub (Piper methysticum) that grows in the South Pacific. It is ingested as a tea or in capsule form. Active ingredients are thought to be kavalactones.
(See also Overview of Dietary Supplements.)
Strong scientific evidence supports use of kava as an antianxiety agent and sleep aid. Mechanism is unknown, although some evidence indicates that kava modulates the gamma-aminobutyric (GABA) pathway. Some people use kava for asthma, menopausal symptoms, and urinary tract infections. Dose is 100 mg of standardized extract 3 times a day.
A 2003 Cochrane review evaluated 11 trials (total of 645 participants) to assess the effectiveness and safety of kava extract in clinical trials for treating anxiety. The meta-analysis concluded that kava extract appears to be an effective option for relieving anxiety compared to placebo (1). This study also concluded that consumption of kava supplements for 1 to 24 weeks appeared safe but suggested a need to study long-term safety. It is unclear how the supplements used in the meta-analysis above was standardized. A more recent review evaluated 7 trials of kava compared to placebo for anxiety symptoms, 2 trials versus prescription antianxiety drugs, and 2 trials to evaluate additional adverse events (2). Compared to placebo, kava had a greater likelihood of response in 3 of the 7 trials and comparable response to prescribed antianxiety drugs. Adverse events did not differ between groups, including hepatotoxicity.
A 2013 randomized controlled trial compared an aqueous kava extract to placebo for generalized anxiety disorder. After 8 weeks, 26% of kava users had remission compared to 6% on placebo. In the kava group, certain genetic traits (GABA transporter polymorphisms) were associated with anxiety reduction (3). However, a 16-week 2020 randomized controlled trial (171 subjects) evaluated kava for generalized anxiety disorder (4). This study found no difference in anxiety reduction between groups, a higher percentage of anxiety remission in placebo groups at the study conclusion, and no evidence of association of genetic polymorphisms with anxiety reduction. Notably, liver enzyme elevation was more frequent in the kava group, although those subjects did not meet criteria for kava-induced liver injury.
Although recent trials found no evidence of liver toxicity (2-4), a number of cases of liver toxicity (including liver failure) in both Europe and the US after taking kava have prompted the FDA to mandate a warning label on kava products (5). Hepatotoxicity may be related to preparation methods or poor quality raw material contaminated with mold that contains hepatotoxins (6). Safety is under continuing surveillance.
When kava is prepared traditionally (as tea) and used in high doses (> 6 to 12 g/day of dried root) or over long periods (up to 6 weeks), there have been reports of scaly skin rash (kava dermopathy), blood changes (eg, macrocytosis, leukopenia), and neurologic changes (eg, torticollis, oculogyric crisis, worsening of Parkinson disease, movement disorders).
Pittler MH, Ernst E: Kava extract for treating anxiety. Cochrane Database Syst Rev (1):CD003383, 2003. doi: 10.1002/14651858.CD003383.
Smith K, Leiras C: The effectiveness and safety of kava kava for treating anxiety symptoms: a systematic review and analysis of randomized clinical trials. Complement Ther Clin Pract 33:107-117, 2018. doi: 10.1016/j.ctcp.2018.09.003.
Sarris J, Stough C, Bousman CA, et al: Kava in the treatment of generalized anxiety disorder: a double-blind, randomized placebo-controlled study. J Clin Psychopharmacol 33(5):643-648, 2013. doi: 10.1097/JCP.0b013e318291be67.
Sarris J, Byrne GJ, Bousman CA, et al: Kava for generalised anxiety disorder: a 16-week double-blind, randomised, placebo-controlled study. Aust N Z J Psychiatry 54(3):288-297, 2020. doi: 10.1177/0004867419891246.
NIH LiverTox: Kava Kava Drug Reference. Accessed 8/20/2018.
Teschke R, Sarris J, Schweitzer I: Kava hepatotoxicity in traditional and modern use: the presumed Pacific kava paradox hypothesis revisited. Br J Clin Pharmacol 73(2):170-174, 2012. doi: 10.1111/j.1365-2125.2011.04070.x.
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of kava as a dietary supplement