Ask the Doctors - What are the risks and benefits of kava?

Dr. Robert Ashley, MD

Note: This column was updated on 12/5/2023. 

Dear Doctor: What are the benefits and risks of taking kava?

Dear Reader: 

That’s a good question with a complex answer. The shrub kava originates from the South Pacific, where Pacific Islanders used it to promote psychological and physical relaxation for medicinal and ceremonial purposes. Within traditional cultures, the root of the plant is crushed, ground and then combined with a mixture of water and coconut milk to make it drinkable. In the naturopathic boom of the 1990s, kava was touted as a safe alternative to other medications used for anxiety. Today, kava is a popular supplement for anxiety, and various brands can be found in any health food store.

The root of the kava plant contains 18 different phytochemicals, or plant-based compounds, known as kavalactones. These compounds alter the conduction of nerve signals, decrease excitatory neurotransmitters, increase the ability of the amino acid GABA to bind its receptors, inhibit the enzyme monoamine oxidase, and reduce uptake of the neurotransmitters noradrenaline and dopamine. All of this is a technical way of saying: Kava can help reduce anxiety. One interesting aspect is that kava binds to a different GABA receptor than benzodiazepines, such as Xanax, Valium, or Ativan.  This aspect may make kava less addictive than these other medications used for situational anxiety and may play a role in helping those who are addicted to other medications.  That being said, consistent users of kava have withdrawal symptoms when they stop taking this supplement. 

A 2003 review of 11 randomized controlled trials with a total of 645 patients assessed kava supplements’ ability to treat anxiety. The studies used varying levels of the kavalactones, from 60 milligrams to 280 milligrams. These doses are significantly higher than what Pacific Islanders traditionally used. The studies varied from one to 25 weeks. Ten of the 11 studies showed a decrease in anxiety compared with placebo. These benefits appeared to be comparable to the effect of tranquilizers such as benzodiazepines and the anxiety drug buspirone. Side effects included nausea, stomach aches, drowsiness and headaches. No liver toxicity was reported, but then, no liver tests were performed.

However, a 2019 study compared kava with placebo for the treatment of generalized anxiety in 171 people. The 16-week trial kava did show a mild benefit compared to placebo, but the affect was not statistically significant, leading the authors to conclude that kava has no long-term benefit for generalized anxiety. In this study, those who took kava had diminished memory compared to placebo and tremulousness. In addition, liver function test abnormalities were more common in those taking kava.

Major liver issues with kava initially led to the herb being banned in many countries. In the early 2000s, more than 100 cases of liver toxicity related to the use of kava had been identified, some leading to liver transplant and some leading to death. There are many reasons for liver damage. For one, kava depletes glutathione, a chief antioxidant, within the liver. It also inhibits enzymes involved in the metabolism of many drugs. Many of the cases of liver toxicity were seen in people who had prior liver disease or used alcohol in addition to kava.

Due to the concerns regarding liver toxicity and kava, there are fewer randomized trials using kava.  The toxicity to kava could be dose dependent and as such, lower doses (less than 240 mg per day) may be safer. Water-based products may be safer than products that are alcohol based. Yet, alcohol-based preparation may be more affective. There is also the risk that some individuals lack the enzyme to help metabolize kava; 99% of Pacific Islanders have sufficient enzyme, Cytochrome P450 2D6 (CYP2D6), to metabolize kava, while from 79% to 88% of Caucasian populations have sufficient enzyme

However, a study of 31 people in Hawaii who were regular kava drinkers showed a significantly greater elevation of two liver enzymes compared with people who were not kava drinkers. Again. this may be related to both the dose and the consistent use of kava. 

Studies have shown that consumption of kava supplements leads to a slower reaction time and an impairment of motor skills. Because it inhibits multiple enzymes and has psychoactive properties, kava likely should not be taken with antidepressants.

In summary, kava may help relieve anxiety in the short term. Nonetheless, the lack of human clinical trials makes it difficult to assess the benefits of kava. This is one of the problems with the assessment of herbs as medicine. The lack of funding for further study of kava, the fears of toxicity and the great disparity between different kava products make a full assessment difficult. I would be hesitant to use it for the short-term relief of anxiety. If one did use kava, I’d look at using doses less than 240mg. Similar to Xanax, Valium, Ativan I would not recommend using kava for the long-term treatment of generalized anxiety. Cognitive behavioral therapy has greater long-lasting benefits for generalized anxiety.

Robert Ashley, MD, is an internist and assistant professor of medicine at the University of California, Los Angeles.

Ask the Doctors is a syndicated column first published by UExpress syndicate.