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

Dear Reader: The kava shrub 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.

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 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.

Note that kava has been banned in the United Kingdom and within Europe due to liver toxicity. More than 100 cases of liver toxicity related to the use of kava have been identified, some leading to liver transplant and others 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.

You may think kava is safe if you don’t have liver disease or are not taking medications metabolized by the liver, but that might not be the case. 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. There is some evidence that kava that is prepared with water is less harmful to the liver than suspensions prepared in acetone or ethanol.

Studies have shown that consumption of kava supplements leads to a slower reaction time and an impairment of motor skills. However, there has been no proof of any decline in cognitive function. Also, because it inhibits multiple enzymes and has psychoactive properties, kava likely should not be taken with anti-depressants.

In summary, kava may help relieve anxiety in the short term. However, due to the severe side effects at its current doses, I would be hesitant to use it for the short term and recommend not using it in the long-term. Cognitive behavioral therapy has greater long-lasting benefits.

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