All products containing kava (Piper methysticum) must carry the TGA label warning "not for prolonged use." This applies to every kava product regardless of dose, extract type or raw material quality.
As this warning does not define a specific time period, to help practitioners interpret and provide explanation to their patients, we recommend reviewing the published human clinical trials for duration and safety data. These should be considered alongside the individual patient (e.g. their health history, alcohol intake, concurrent medications and liver health).
Key literature reporting duration of kava use and safety data:
Volz & Kieser (1997)
24 weeks, 210 mg kavalactones/day (acetonic extract), n=101.
Adverse events: Rare, and fewer than placebo, with 2 cases of stomach upset rated possibly related. No clinically relevant changes in liver enzymes and no withdrawal symptoms.
Sarris (2020): 16 weeks, 240 mg kavalactones/day (aqueous extract, noble Vanuatu cultivar), n=171.
Adverse events: Kava was well tolerated overall, although mild liver enzyme elevations were more frequent at week 16 (24% vs 8%), particularly in heavier drinkers. No participant met criteria for herb-induced liver injury. Poor memory and tremor were more frequent than with placebo.
Boerner (2003): 8 weeks, 120 mg kavalactones/day (ethanolic extract), n=129, compared with buspirone and opipramol.
Adverse events: Well tolerated. Adverse event rates didn't differ significantly between groups.
Sarris (2013): 6 weeks, 120 to 240 mg kavalactones/day (aqueous extract), n=58.
Adverse events: No significant adverse events, no liver function differences from placebo, and no addiction or withdrawal effects.
Pittler & Ernst (2003) (Cochrane): 12 trials, 1 to 24 weeks.
Adverse events: Mild, transient and infrequent. Kava was considered relatively safe for short-term use, with long-term safety studies still required.
Taking a conservative approach, consistent with our guidance on liver safety, we recommend additional practitioner oversight for use beyond 8 weeks. This includes reviewing alcohol intake and concurrent medications and considering baseline and follow-up liver function tests where appropriate.
Additional relevant literature includes:
Pittler MH, Ernst E. Kava extract versus placebo for treating anxiety. Cochrane Database of Systematic Reviews. 2003;2010(6).
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. 2018;33:107–17.
Bian T, Corral P, Wang Y, Botello J, Kingston R, Daniels T, Salloum RG, Johnston E, Huo Z, Lu J, Liu AC, Xing C. Kava as a Clinical Nutrient: Promises and Challenges. Nutrients. 2020 Oct 5;12(10):3044.
Soares RB, Dinis-Oliveira RJ, Oliveira NG. An Updated Review on the Psychoactive, Toxic and Anticancer Properties of Kava. J Clin Med. 2022 Jul 12;11(14):4039.
Teschke R, Sarris J, Schweitzer I. Kava hepatotoxicity in traditional and modern use: the presumed Pacific kava paradox hypothesis revisited. Br J Clin Pharmacol. 2012 Feb;73(2):170-4.