A popular herbal supplement can interfere with many medications, including birth control

• Many supplements are advertised as a healthy addition to any diet.
• Some supplements, however, can interfere with medications including antibiotics and birth control.
• St. John's wort is an herbal supplement advertised for depression and inflammation relief, but studies suggest it can be dangerous.

They're colorful, chewable, and more affordable than a doctor's visit. And if you believe some of their claims, supplements can do everything from giving you an energy boost to helping you lose weight. At the very worst, your daily tablet can't do any harm - right?

Not so fast. A growing body of research suggests that some supplements can carry real health risks that range from vomiting to negative interactions with existing medications and even an increased risk of cancer and death.

St. John's wort, an herbal supplement sold widely in the US and advertised for everything from helping with depression to relieving inflammation, can severely curb the effectiveness of several important pharmaceutical drugs - including antibiotics, birth control, and antiretrovirals for infections like HIV. The herb speeds up their breakdown in the body, potentially rendering the medications useless.

'Most people don't consider it a medication'

When Pouya Jamshidi, a resident at Weill Cornell Medical College, delivered his first baby, he had to quarantine the child after it was discovered that the mother had been taking St. John's wort and re-contracted a highly contagious infection as a result.

"The trouble is most people don't consider it a medication because you don't need a prescription for it, and so she didn't tell us," Jamshidi told Business Insider.

Although the pregnant woman had been incredibly cooperative with Jamshidi and his team throughout her pregnancy, she didn't realize that the herbal supplement was counteracting the effects of the antibiotics she was taking to prevent the tuberculosis from coming back.

"It basically over-metabolized the antibiotics so they weren't in her system in the correct dose," Jamshidi said.

In 2000, the National Institutes of Health published a study showing that St. John's wort could severely curb the effectiveness of several important pharmaceutical drugs by speeding up their breakdown in the body. The findings prompted the US Food and Drug Administration to warn doctors about the herbal remedy, but that did little to stem public sale or consumption of it.

Over the past two decades, US poison-control centers have gotten about 275,000 reports - roughly one every 24 minutes - of people who reacted badly to supplements; a third of the reports were about herbal remedies like St. John's wort.

When Jamshidi and his team realized the pregnant woman's tuberculosis had returned, they asked her if she had started any new medications. She said no, but the next day she arrived at the clinic with a small bottle of St. John's wort.

She said she had been taking the herbal remedy for the feelings of depression she experienced after her last pregnancy. Although some small studies initially suggested St. John's wort could have benefits for people with depressive symptoms, the NIH researchers failed to find enough evidence to support that.

As a result of her tuberculosis, Jamshidi's patient had to be isolated to ensure the infection didn't spread. She spent the last three months of her pregnancy alone.

"It was miserable - she was isolated for all that time, and then she couldn't even hold the baby," said Jamshidi.

He believes one of the reasons many people end up in emergency rooms after taking supplements is that the quantities of active ingredients in them can vary dramatically. A 2013 study published in the journal BMC Medicine found that doses of ingredients in supplements could even vary from pill to pill - which poses a significant hurdle for doctors trying to treat a negative reaction.

"There are other medications that can have side effects, but patients come in and tell you the dose, and you can reverse it," Jamshidi said. "But with supplements, you don't know what you're dealing with."

Steve Mister, the president and CEO of the Council for Responsible Nutrition, a Washington, DC-based trade organization representing more than 150 supplement and other companies, disagreed. He told Business Insider that the vast majority of supplements are safe and consumers should feel confident taking them.

"Supplements are products that are intended to supplement the diet," said Mister. "Consumers should expect that these are things that'll help with their overall well-being and their overall health."

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