Benefits
Calm and everyday stress support
In a pooled analysis of 6 placebo-controlled trials in 345 people with anxiety, kava extract lowered Hamilton anxiety scores about 5 points more than placebo, and a 6-week trial in people with generalized anxiety also favored kava. But two larger trials found kava no better than placebo: 391 adults with anxiety over 4 weeks, and 171 people with generalized anxiety over 16 weeks.
Sleep quality and feeling rested
In a 4-week randomized, double-blind trial in 61 adults whose sleep was disturbed by anxiety, tension or restlessness, 200 mg/day of the kava extract WS 1490 improved self-rated sleep quality and feeling rested after sleep more than placebo. However, a review of 14 herbal insomnia trials, kava among them, found no significant benefit over placebo for any herb.
Mechanism of action
GABA-A receptor modulation
In lab tests on human GABA-A receptors, kavain, the main kavalactone, boosted the receptor's response to GABA, the brain's main calming messenger. It did not act through the benzodiazepine binding site. How this translates to effects in people is not fully known.
Inhibition of drug-metabolizing liver enzymes
In human liver tissue tested in the lab, kava extract and its kavalactones inhibited several cytochrome P450 enzymes (CYP2C9, CYP2C19, CYP2D6 and CYP3A4) that break down many medicines, which is one way kava could change drug levels.
Clinical trials
Systematic review and meta-analysis of randomized, double-blind, placebo-controlled trials of single-ingredient oral kava extract. (Pittler et al. 2003, Cochrane Database Syst Rev)
11 trials with 645 participants with anxiety; 6 trials (345 people) pooled on the Hamilton Anxiety scale.
Kava extract lowered Hamilton Anxiety scores by an average of 5.0 points more than placebo (95% CI 1.1 to 8.8). Side effects reported in these short trials were mild, transient and infrequent; the authors called for research on long-term safety.
Phase III, multi-site, randomized, double-blind, placebo-controlled trial of a water-based kava root extract standardized to 120 mg kavalactones twice a day for 16 weeks. (Sarris et al. 2020, Aust N Z J Psychiatry)
171 adults with diagnosed generalized anxiety disorder not taking medication, Australia.
Anxiety fell no more on kava than on placebo (difference of 1.37 points favoring placebo, p = 0.25), and 17.4% on kava vs 23.8% on placebo ended with a very low anxiety score. Poorer memory, tremor and liver test abnormalities were more frequent on kava, though no one met criteria for herb-induced liver injury.
Randomized, double-blind, placebo-controlled trial of a water-based kava extract (120 or 240 mg kavalactones per day by response) for 6 weeks after a 1-week placebo run-in. (Sarris et al. 2013, J Clin Psychopharmacol)
75 adults with generalized anxiety disorder enrolled; 58 analysed.
Hamilton anxiety scores fell more on kava than placebo (P = 0.046, moderate effect size), and 26% vs 6% ended with a very low anxiety score. Headaches were more common on kava; liver tests did not differ between groups.
Multicenter, randomized, double-blind, placebo-controlled trial of 200 mg/day WS 1490 for 4 weeks. (Lehrl 2004, J Affect Disord)
61 adults with sleep disturbances linked to anxiety, tension and restlessness.
Both main outcomes, self-rated sleep quality (P = 0.007) and feeling rested after sleep (P = 0.018), improved more on kava than placebo, as did the psychic anxiety subscore. No drug-related side effects or lab changes were reported.