WASHINGTON?The popular herbal supplement kava may be linked to serious liver injury, the Food and Drug Administration warned Monday, urging consumers to see a doctor at the first sign of symptoms.

People who already have liver problems, or who take medications that can harm the liver, should ask a doctor before taking kava, the FDA said.

The FDA began investigating the herb after a kava user suddenly required a liver transplant. European health officials report 25 similar cases of liver toxicity.

As a result, Canada has urged consumers not to take kava until the safety question is settled; sales were halted in Switzerland and France and suspended in Britain.

The FDA said Kava users should consult a doctor if they experience any possible symptoms, including jaundice, brown urine, nausea or vomiting, light-colored stools, unusual fatigue, stomach or abdominal pain or loss of appetite.