After weeks of investigating the popular herbal supplement kava kava, the U.S. Food and Drug Administration (FDA) announced this week that the substance may be linked to serious liver damage. Although more research is required to prove if kava kava actually causes symptoms of severe liver disease, the FDA issued the warning after several European reports emerged detailing the supplement's association with liver damage. Nearly thirty cases of liver toxicity, six involving liver failure, were reported in Germany and Switzerland. A spokesperson for the FDA said the warning is necessary because of the supplement's potential to cause the severe side effects.

Sales of kava kava have already been halted in France and Switzerland and suspended in Britain. Last year, German pharmaceutical giant Merck recalled all of the company's products that contain kava kava.

In the United States, dietary supplement manufacturers are not required by law to prove their products are safe or effective before distributing them. Sales may only be halted after a supplement is proven dangerous.