These 3 common herbal supplements can cause dangerous drug interactions or liver damage, a researcher says

• Pharmacies are full of natural supplements, which tout health claims like better sleep and immunity.
• But natural supplements aren't necessarily good for you, and some might cause harm.

Take a walk down the supplement aisle and you'll find hundreds of multi-colored bottles advertising health benefits ranging from improved muscle mass, to virility, immune defense, and sleep.

But lurking behind these grandiose claims are sometimes dangerous side effects, especially when some supplements are combined with prescription medication.

Even "natural" or "herb" supplements can have dangerous drug interactions, Dr. Bill Gurley, principal scientist at the National Center for Natural Products Research at the University of Mississippi, told Insider.

"You'll hear a lot of consumers go, 'oh, it's natural. It's gotta be good for me,'" Gurley said. But that's not necessarily the case.

Gurley shared three common herbal supplements that could be dangerous.

St. John's Wort can make your prescription medication ineffective

St. John's Wort is a yellow-flowered plant native to Europe. Some people promote St. John's Wort as a treatment for depression, ADHD, or menopause, according to the National Institutes of Health.

Taken on its own, St. John's Wort is harmless, Gurley said, "but don't take it with other conventional medications."

That's because St. John's Wort can weaken the effects of prescription medications.

For example, St. John's Wort can make birth control less effective, leading to "miracle babies," Gurley said.

According to the NIH, people who take prescription medications including antidepressants and HIV medications could also be at risk of dangerous side effects when combined with St. John's Wort.

Goldenseal can cause toxic amounts of medication to enter your bloodstream

While St. John's Wort can make some medications less effective, other supplements— like goldenseal — might make prescription medications too potent, Gurley said.

Goldenseal is native to North America, and is touted today as a remedy for colds, hay fever, ulcers, and digestion issues like diarrhea and constipation, according to the NIH.

But taking goldenseal can change the way your body processes medication, said Gurley. The result is that more of your medication can get into your bloodstream, potentially to a toxic level.

Green tea extract can damage your liver

While drinking green tea is safe, green tea extract can cause health issues — notably liver injury.

Green tea extract, often taken in pill form, is marketed as improving mental alertness, aiding in weight loss, and for helping headaches and digestive symptoms.

But green tea extract has been linked to liver injury, including in formulations of over-the-counter weight loss products. While it's relatively uncommon, the NIH advises that people who have a liver disease should not use green tea extract or consult with a doctor.

Too much of any supplement can be dangerous

While most herbal supplements on their own are not dangerous, Gurley said, any supplement that's taken in much higher quantities than what's advised can pose health risks.

Quoting the father of toxicology, Paracelsus, Gurley said, "the dose makes the poison."