A herb in the balance

Two years ago, the UK government banned kava, a herbal remedy for treating anxiety. A suspicion had emerged that it might cause liver damage. The ban incensed proponents, some of whom decided to take the government to court over the matter. Now the Medicines and Healthcare products Regulatory Agency (MHRA) is reconsidering the decision; the organisation has recently invited interested parties to submit new evidence.

Kava is a plant (Piper methysticum) from the South Sea, where it has been used as a medicine for centuries. Rigorous clinical trials over the past two decades have demonstrated that it is effective in reducing anxiety. Kava therefore had become very popular. But the "kava-boom" came to a halt when cases of severe liver problems emerged. Eighty-four cases have now been associated with kava worldwide. Nine patients have suffered irreversible liver failure, and six individuals have died. None the less, proponents, including those organised in the International Kava Executive Council, insist that the evidence is inconclusive, pointing out that such adverse effects are extremely rare - only about one case per 50 million kava users.

Several new theories might explain what is really going on. In most of the cases, experts identified other possible causes for the liver damage. Many of the affected patients also consumed alcohol or took drugs known to damage the liver. The other patients could have suffered from liver conditions related to diseases such as infectious hepatitis. And some people will always experience liver problems apparently out of the blue.

Another theory holds that the modern manufacturing process for kava supplements is to blame. Natives from the South Sea make their kava drink essentially by dissolving the root in water. Kava supplements, however, are extracted with solvents which take out toxic constituents from the plant which are absent in the traditional kava drink. New evidence suggests that habitual kava users in the South Sea show no signs of liver problems even though they take rather high doses.

Other experts suspect that the huge popularity of kava supplements created so much demand that people started processing parts of the plant that were never meant to be used. This mistake, they think, led to products with toxic constituents not normally contained in quality products. This theory could explain why kava was used for such a long time without problems, and only when sales boomed did problems emerge.

Finally, some researchers believe that there could be a genetic explanation. Natives of the South Sea might be protected from liver damage simply because they are genetically different from us. In fact, the vast majority of Caucasians have nothing to fear. According to this school of thought, only a very small group of people afflicted with a genetic abnormality are at risk.

Meanwhile, three new clinical trials confirm the effectiveness of kava in relieving anxiety, which brings the total number of trials to 12. Several independent experts are now sure that the benefits of kava outweigh its risks. They also point out that conventional drugs with similar anxiolytic properties, such as Valium, are at least as harmful as kava.

In the coming months, the kava debate is set to reignite. The MHRA has already stated that kava poses "a rare but serious risk to public health". The First International Kava Conference, which took place in December 2004 in Fiji, arrived at the opposite conclusion: "We see no grounds for continuing bans and restrictions [and] call for their immediate removal." Watch this space.

· Edzard Ernst is professor of complementary medicine at the Peninsula medicine school at the universities of Exeter and Plymouth.

Source The Guardian
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