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5 Risky Herbal Supplements

Even though they're natural, some herbal supplements can be dangerous.


Kava (Piper methysticum) can reduce anxiety, and for some it has worked as well as prescription anti-anxiety drugs. But it may take up to eight weeks to work. In women experiencing anxiety in menopause, kava has worked in as little as one week, according to the National Institutes of Health.   

However, the National Institutes of Health and the FDA urge people not to take kava because of the risk of serious illness, liver damage, and death even when taken for only a short time at normal doses. Kava use has led to liver transplants and death in one to three months. "Heavy kava use has been linked to nerve damage and skin changes," Weil tells WebMD.

Kava can worsen depression and is not safe for women who are pregnant or breastfeeding. Because the herb has effects similar to those of alcohol, the two should not be combined.

A number of prescription drugs should not be combined with kava. The two drugs with the potential for greatest drug interactions are alprazolam (Xanax) and sedatives.

Weil only recommends kava for a maximum of three to four weeks in patients with healthy livers. "I do not recommend kava for people at risk for or who have liver disease, regularly drink alcohol, or take drugs with known adverse effects on the liver, including statins and acetaminophen."

Other experts have completely ruled kava out. "I prefer to use herbs that have a good risk-to-benefit ratio, and for kava that's no longer true," Fugh-Berman says.


Comfrey (Symphytum officinale) has "a well-deserved reputation for healing injured tissues," such as wounds, bruises, sprains, bone fractures, and the swelling and inflammation that can go along with them, Weil tells WebMD. But because of the risk for severe liver and possibly lung damage, "comfrey should never be taken by mouth," Weil says.

The FDA recommended in 2001 that manufacturers remove comfrey products from the market. Still, comfrey is easy to find.

"My local coffee shop serves comfrey tea, and when I told them it was a liver-toxic herb, they said, ‘Oh, we sell a lot of it,'" Fugh-Berman says.

Weil recommends applying comfrey to wounds that don't heal easily, including open bedsores and diabetic ulcers. However, the U.S. Pharmacopeia, a scientific organization that sets standards for dietary supplements, advises against using comfrey on broken skin, as the toxins that may affect the liver can be absorbed. 


Chaparral (Larrea divaricata, Larrea tridentata) is said to reduce pain, inflammation, and skin irritation.  However, there is little evidence for this, Weil tells WebMD.  Chaparral has also been promoted as a cancer-fighting herb, but according to the American Cancer Society, there is no evidence supporting that, either.

Easily found online in many forms, chaparral has been listed in the FDA's poisonous plant database since 1997 because of the risk of severe -- and in some cases, irreversible -- liver damage.

According to the American Cancer Society, chaparral can cause serious drug interactions with some prescription and over-the-counter drugs, including blood thinners; anti-inflammatory drugs, such as aspirin, ibuprofen, and naproxen; diabetes medications, and certain antidepressants

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