7 POPULAR DIETARY AND HERBAL SUPPLEMENTS THAT CAN BE TOXIC IN HIGH DOSES

Dietary supplements are more popular than ever. Vitamins, minerals, herbs, enzymes and other botanicals are now a mainstay in medicine cabinets.

Three in four Americans take at least one dietary supplement, according to the U.S. Food and Drug Administration. Many people take them with the intention to boost overall health or as an alternative to pharmaceutical drugs — but supplements are not medicines and “are not intended to treat, diagnose, prevent, or cure diseases,” the FDA says.

Dietary supplements are regulated as a subcategory of food, so not in the same way as drugs, which undergo rigorous safety and efficacy testing. However, supplements can still have powerful impact in the body and cause side effects — including organ damage in high doses — and interact with medications.

In a 2022 study published in the journal Liver Transplantation, researchers found that between 1995–2020, the number of people in the U.S. with herbal and dietary supplement-induced liver damage who were waiting for transplants increased eightfold.

"People think supplements cannot hurt, but they can," Dr. Julia Adamian, an internist at NYU Langone Health, tells TODAY.com.

However, certain supplements warrant more caution than others due their potential to cause side effects, interactions or toxicity.

"Some herbs and supplements are just more potent, and it makes them inherently more risky," Dr. Zachary Mulvihill, integrative medicine expert at Weill Cornell Medicine and NewYork-Presbyterian, tells TODAY.com.

It's important to be aware of the risks and always consult with a doctor before trying these supplements, experts say.

Vitamin A

Vitamin A is crucial for healthy vision, skin and immune function. It's a popular supplement, often marketed for eye health. However, in high doses, vitamin A can do harm.

Vitamin A is fat-soluble, which means it's stored in the fatty tissues and liver, and excess vitamin A builds up in the body —unlike water-soluble vitamins, which get excreted in urine.

“You can become vitamin A-toxic if you’re exceeding the daily recommended intake (DRI) on a chronic basis,” Dr. Joel Mason, professor of medicine and nutrition at Tufts University and Tufts Medical Center, tells TODAY.com.

The "therapeutic window" of vitamin A — the difference between the amount you need and the amount that causes toxicity — is relatively narrow, says Mason.

The DRI for vitamin A for adults is 700-900 micrograms, per the National Institutes of Health, whereas the amount that can lead to toxicity is just over 3,000 micrograms, says Mason.

Vitamin A toxicity can cause liver injury, bone pain and skin changes. In severe cases, vitamin A overdose can lead to organ failure. In pregnant women, vitamin A toxicity can cause birth defects.

Avoid vitamin A if you are pregnant, have liver or kidney disease, or take blood thinners, and always talk to your doctor before starting a supplement.

Vitamin B6

Even though water-soluble vitamins, such as B vitamins, in excess amounts are peed out, taking them in supplement form can still be harmful. "One of the best examples is vitamin B6, or pyridoxine," says Mason.

Vitamin B6 plays an important role in over 100 enzyme reactions involved in metabolism and you need it to maintain health. But taking high doses of vitamin B6 for a year or longer is linked to nerve damage — specifically, peripheral neuropathy, or a loss of sensation in the extremities, Mason notes. This can cause difficulty controlling body movements.

"Some people have become pretty disabled as a result of mega-dosing vitamin B6," says Mason.

The DRI for vitamin B6 is 1.3–1.5 milligrams for adults, per the NIH. Consuming upwards of 100 milligrams a day can lead to toxicity. B vitamins are often added to multivitamins and proprietary supplement blends for energy or metabolism, says Mulvihill, so it's important to be aware of what you're taking.

St. John's Wort

St. John's wort is an herb that's most commonly used for depression, says Mulvihill.

"It's a tricky one because St. John's wort messes with the enzymes in the liver in a way that increases the breakdown of many medications," says Mulvihill.

This can cause the body to metabolize the drugs rapidly, which can weaken the effects of many medicines, including antidepressants, birth control pills and blood thinners, according to the NIH's National Center for Complementary and Integrative Health.

One medicine in particular is especially risky when taken with St. John's wort — a type of antidepressant called selective serotonin re-uptake inhibitors (SSRIs). But rather than having a weakening effect, mixing St. John's wort and SSRIs can cause a life-threatening increase in serotonin in the body, per the Cleveland Clinic.

“I've found that it’s just not worth it of because of the potential for interactions," says Mulvihill. Avoid St. John's wort if you take any psychiatric medications and always talk to your doctor before starting herbal supplements.

Black Cohosh

Black cohosh is an herb commonly used for menopause symptoms, says Adamian. Supplements containing black cohosh are often promoted to help with hot flashes and night sweats — however, these benefits haven't been proven, and the herb has potential risks, TODAY.com previously reported.

Namely, black cohosh can increase liver enzymes, which "can lead to (drug-induced) autoimmune liver injury," says Adamian.

Symptoms of liver problems include pain in the upper right abdomen, loss of appetite, fatigue, itchy skin, dark-colored urine, pale stools, and yellowing of the skin or the whites of the eyes.

The purity and strength of black cohosh supplements can vary, and they may contain ingredients not listed on the label, per the Cleveland Clinic.

If you have any underlying conditions affecting your liver, it’s best to avoid black cohosh, the experts note.

“Anything that has the potential to raise liver enzymes certainly needs to be taken under supervision,” says Mulvihill.

Turmeric

Turmeric, regarded as one of the healthiest spices, has been used for culinary and medicinal purposes for thousands of years. The health effects are often attributed to curcumin, the most biologically active compound in turmeric, says Mason.

"Turmeric is well known for its anti-inflammatory properties, and the use of supplements has increased rapidly over the last few years," says Adamian. Turmeric supplements are often marketed for inflammation, joint pain and heart health, per the NCCIH.

Most turmeric supplements are formulated with concentrated curcumin and black pepper, which increases the absorption of curcumin in the body by twentyfold, NBC News reported.

Unlike the turmeric you cook with, supplements are ultra-concentrated and provide you a very high dose, Mulvihill notes. Combined with black pepper, this can overwhelm the liver. In rare cases, turmeric supplements can cause liver injury or failure.

“It’s only safe to use if it is used at a lower dose (less than 2,000 milligrams per day) for up to seven weeks,” says Adamian.

Always talk to your doctor before starting turmeric or curcumin supplements — and try to incorporate the spice into your diet before popping a pill, the experts note.

Kava

Kava is an herbal remedy often promoted for stress relief and relaxation, the experts note. It's derived from a shrub native to the South Pacific and sold as a supplement or added to drinks.

It's often used for anxiety due to its sedative effects. "Kava tends to act pretty quickly and be potent," says Mulvihill.

While some people may find it helps anxiety, there isn't enough evidence that kava is helpful for generalized anxiety disorder or other health conditions, per the NCCIH — and there are risks.

High doses of kava may cause dry, scaly skin and neurological symptoms. Mulvihill adds that he's "seen kava raise people’s liver enzymes, and there have been case reports of liver toxicity with supplements," Rarely, these have been serious or fatal.

Kava has also been shown to interact with other drugs and supplements, which may lead to serious health consequences, the FDA said in a review of research on kava published in 2020.

Always talk to your doctor before trying kava, and never mix kava with alcohol or medications with sedating effects.

Green Tea Extract

Drinking green tea has been linked to a number of health benefits, says Adamian. And green tea extract, rich in antioxidants, is a popular supplement promoted for weight loss, cholesterol and heart health.

There have been many studies on green tea extract, but there isn't enough evidence to make conclusions about the health benefits, per the NCCIH.

Green tea extract can cause unpleasant gastrointestinal side effects for some people, including nausea, abdominal pain, vomiting and diarrhea. Plus, most green tea pills contain caffeine, which can cause jitteriness, a fast heartbeat or sleeping issues, the experts note.

"In high doses, more than 800 milligrams, or with prolonged use, it can also cause liver toxicity," says Adamian. Green tea may also interact with other medications or herbs in harmful ways.

The experts warn people to be cautious around green tea-containing supplements marketed for weight loss.

The Bottom Line: Talk to a Doctor

If you're considering taking a vitamin, mineral, herb or other dietary supplement, always consult your doctor first.

"What makes some (supplements) dangerous is the fact that most people think they cannot hurt and are always safe, so the suspicion is that a large amount of patients do not mention it to their doctor," says Adamian.

The potential for a supplement to help or cause harm also depends on a person’s underlying health, Andrea Wong, Ph.D., senior vice president of scientific and regulatory affairs at the Council for Responsible Nutrition, the leading trade group for dietary supplements, tells TODAY.com.

People who have liver or kidney issues, are pregnant or breastfeeding, receiving chemotherapy, or take multiple prescription medications should be especially careful to avoid taking supplements unless directed by their doctor.

Always opt for products from trustworthy, reputable brands with third-party testing certifications or seals, says Wong. "Look for ones that don't overstate their benefits. ... Dramatic claims of big, overnight changes would be a red flag," Wong advises.

The experts also warn against buying trendy supplement blends online or through social media. “If it’s from a brand that hasn’t been around for long, and it’s a proprietary formula or they’re not fully disclosing what’s in it, stay away from that stuff,” says Mulvihill.

Finally, supplements are meant to do exactly that: supplement your diet to fill gaps and help you meet nutritional needs. "Sometimes there's a misconception that they're a shortcut to a healthy diet (and) lifestyle. ... Supplements can complement but definitely not replace those things," says Wong.

This article was originally published on TODAY.com

2025-06-11T17:17:14Z