BACKGROUND:In January 2011, a systematic review of kava research concluded that it is effective for generalised anxiety. Although only six studies were identified, the majority found evidence of benefit.
This evidence may trigger renewed anxiety about the safety of kava. After first becoming popular as a herbal remedy, numerous cases of liver toxicity were reported, including some deaths. This led to several countries banning kava in 2002, with it being voluntarily withdrawn from the Irish market.
Kava, or kava kava, is a popular social drink in the South Pacific islands made from Piper methysticum. Early European explorers called it “intoxicating pepper”.
During the 1990s, kava’s reputation for relieving stress and anxiety led to huge demands for kava remedies. After being banned, kava producers fought to reverse bans due to the economic hardships caused in their countries.
The World Health Organisation investigated the issues, and its report contributed to many bans being lifted.
EVIDENCE FROM STUDIES
Further investigations into the liver problems highlight some of the challenges in regulating herbal remedies.
The benefits of kava for generalised anxiety are real, but so too are the concerns about liver damage. Thankfully, the incidence of liver damage is rare and limited to some types of products.
One early theory about the liver problems was the use of alcohol or acetone to extract the plant for Western products, while water was used traditionally.
However, liver problems have been reported with traditionally prepared products and those prepared with other solvents. Additionally, contamination or adulteration does not seem to be the problem.
Another suggestion was that some people were genetically predisposed to liver problems with kava. However, people from around the world with various ethnic origins have had adverse effects.
Other genetic factors were proposed, but these are no longer thought to explain the problem.
PROBLEMATIC ASPECTS
Currently, most of the evidence for kava toxicity points towards two general issues. One is the plant material itself. In the South Pacific islands, more than 200 varieties or cultivars of Piper methysticum are known.
These are divided into four groups, of which the “noble cultivars” have been used safely for generations. The remaining groups are not used for kava beverages, but in the 1990s were exported for herbal remedies primarily because they were less expensive.
For this reason, the government of Vanuatu, one of the major producers and exporters of kava, passed legislation allowing only noble cultivars to be exported.
However, other governments do not have similar legislation.
The part of the plant used is also important. Traditionally, only the underground parts (roots and rhizomes) were used. These were peeled, and the core used in beverages. In the rush to supply increased demands, the discarded peel was exported. Some products were made using stems and other aerial parts as these were one-tenth the price of roots. Also, plants were used traditionally only after they were five years old. During peak kava demand, plants one to two years old were harvested.
All these factors would change the compounds present in the extracts, leading to some batches containing liver toxins.
The second general problem identified has to do with those taking kava. The chance of getting liver problems was six times higher when people took other medicines or herbal remedies at the same time. Alcohol intake might also increase the risk of toxicity, but the evidence here is not as clear cut.
Also, four out of every five people who experienced adverse effects were taking higher doses for longer periods than traditionally recommended.
RECOMMENDATIONS
Kava highlights the importance and complexity of regulating herbal remedies. Some South Pacific islands have responded by introducing strict laws for exporters and producers. Many Western countries have lifted their bans and introduced strict import and sales regulations. However, a range of different products remains available.
This month, independent investigators involved in kava research issued guidelines for its use. They recommended that only products made from the peeled roots and rhizomes of noble cultivars be used.
Water extracts are preferable since that is the traditional method of preparation. Other medications or alcohol should not be used at the same time. A safe dose has not been determined, but 60-120mg kavalactones daily for no more than three months is commonly recommended.
Finally, anyone with liver problems should not use kava. Kava is traditionally used as a social beverage much like alcohol. It causes relaxation and drowsiness, and therefore kava should never be used when driving or operating machinery.
Dónal O’Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University
