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Kava is an herbal supplement used mainly for its calming psychoactive effects. It is a traditional drink in Oceania that has been used for centuries. It has also been linked to liver toxicity and cases of liver failure and even death. However, the liver toxicity of kava is extremely controversial – this controversy, however, reflects the various narratives that we see surrounding “natural” products and can be very instructive.

A recent Tik Tok video warns of the liver toxicity of kava, and the comments are filled with these dueling narratives. The pro-kava camp is well reflected by this article: “Kava Liver Damage Myth Debunked by New WHO Study.” Yet many medical outlets still warn of the potential for liver damage. The truth is somewhat complex, and is not reflected either in the “debunked myth” narrative or the “never take kava” narrative. Rather, let me (unsurprisingly) frame the controversy as a science-based medicine narrative.

Background

Kava is the common name for the plant Piper methysticum in the pepper family. Extracts from this plant, referred to as either kava or kava kava, have been used for at least centuries, possibly thousands of year, in Oceania. More recently kava extracts have been marketed as herbal supplements in pill, powder, or drink (herbal tea) form.

Starting in the 1990s there were reports of liver failure, starting in Europe, in people taking kava products. Initial case reports, case series, and reviews found that such cases are uncommon but usually extremely serious, with fulminant liver failure leading to the needs for transplant or death in some cases. This lead to many national bans on kava products and general warning away from its use.

However, this only lead to controversy, as many traditional users and kava promoters cast doubt on the evidence. A 2007 WHO review (not a study), the one referenced above, came to some interesting conclusions (none of which amount to debunking a myth). They reference a single 2004 epidemiological study that found no association between regular kava use in Oceania with liver disease, even in daily users. However they also cite the extensive evidence of individual cases of liver failure associated with the use of kava products.

There are two primary issues here. One is the difference in preparation of kava. Traditional preparations use a water extract, and there are many reasons to hypothesize that the water extract version of kava is safer. It contains lower doses of active ingredients, may contain some protective chemicals (like glutathione), and does not contain ingredients that may cause drug-drug interactions with kava or exacerbate its liver toxicity. If we look at the case reports of liver damage, most (but not all) are in people who used kava products extracted with alcohol, not water, although there are a few cases that used water extracts.

The second issue is that the data is all muddy with lots of confounding factors. As the WHO reports says: “There are several possible reasons why hepatotoxicity may occur with kava, such as dose, variety of kava, plant parts used, or type of extract. It is likely that the main problem is related to the chemical composition of the kava product taken.” Also we have poor control in terms of the total dose of various active ingredients, contaminants, adulterants, and drug-drug (including herbal products) interactions.

At present it is fair to say that there is potential liver toxicity from kava products. However, the traditionally prepared water extracts are probably safe as used, although it is difficult to make a firm conclusion from one study. There is still a strong case to be made for rare liver toxicity from kava products prepared for the western market, mainly in pills and tablets.

However, all the reasons given by kava proponents to doubt that kava itself is causing liver damage is in reality an indictment of the supplement industry itself. First, if you get liver failure, it probably doesn’t matter much to you if it was from the product itself, a contaminant, substitution, or interaction.

These are also not defenses of herbal products in general or kava in particular. They indicate the real risk of herbal products – they are poorly regulated, examined, and understood. They are rife with contaminants and substitutions and have poorly regulated and measured dosages. It is not rational to use these limitations and risks of herbal products to fend off evidence of toxicity because they introduce uncertainty. The uncertainty is the problem.

Further, as we see in the Tik Tok comments and in kava defenders, the point is often made that the toxicity of western brands of kava says nothing about the risks of traditional use. But also – the safety of traditional use says nothing about the safety of western kava products where preparations are different and doses tend to be more concentrated. It cuts both ways.

In the end there is still reason to be cautious about using kava products (outside traditional use). Herbal products are poorly researched and regulated drugs. They have real drug risks and side effects. Kava is a great example of why herbal products should not be considered generally safe.

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  • Steven Novella

    Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.

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Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.