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 and National Institutes of Health (NIH): Kava.)
Claims
Kava is used 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.
Evidence
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 this meta-analysis 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. Thus, this casts doubt on the use of kava for generalized anxiety disorder.
Adverse Effects
A number of cases of liver toxicity (including liver failure) in both Europe and the US (5) after taking kava have prompted the US Food and Drug Administration (FDA) to mandate a warning label on kava products. 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 a 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).
Drug Interactions
Kava may prolong the effect of other sedatives (eg, barbiturates, benzodiazepines), which could affect driving or other activities requiring alertness.
Kava may intensify the effect of anesthetics.
Kava may cause liver damage if taken with hepatotoxins.
(See also table Some Possible Dietary Supplement–Drug Interactions.)
References
1. Pittler MH, Ernst E: Kava extract for treating anxiety. Cochrane Database Syst Rev (1):CD003383, 2003. doi: 10.1002/14651858.CD003383
2. Smith K, Leiras CComplement Ther Clin Pract 33:107-117, 2018. doi: 10.1016/j.ctcp.2018.09.003
3. 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
4. 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
5. LiverTox: Clinical and Research Information on Drug-Induced Liver Injury [Internet]
6. 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
More Information
The following English-language resource 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
