A version of column was published in USA Today on November 20, 2013.

I once diagnosed a patient with high cholesterol, and prescribed him a medicine commonly known as a statin.   When I saw him months later for follow-up, he admitted that he didn’t fill the prescription.

“I took red yeast rice capsules instead,” he said.

When I asked him why, he told me that he was wary of statins’ long list of side effects and felt taking a “natural,” over-the-counter cholesterol-fighting supplement was safer.

When it comes to herbal supplements, I generally inform patients that most have little evidence to suggest that they actually work, but leave the ultimate decision of whether to take them to patients.  But given the results of recent studies, I wonder if patients are better off avoiding these supplements altogether.

Americans spend $5 billion a year on pills like echinacea to ward off colds, ginkgo biloba to improve memory, or black cohosh to improve postmenopausal hot flashes. There are over 29,000 herbal products sold throughout North America, with about half of Americans using some form of alternative medicine. Many believe that since these products are promoted as natural or organic, and legally sold and marketed, that they are safe.

That’s not necessarily true.  While smaller studies have previously suggested that herbal supplements are often not what they seem, an October 2013 study from BMC Medicine used DNA analysis to provide the most definitive evidence to date.  Researchers looked at 44 randomly selected supplements, and found that one-third had no trace of the plant advertised on the label.  Consider two bottles of St. John’s wort, for instance, used to treat depression.  One contained pills that had no evidence of the advertised herb, while the other substituted another plant that happened to be a known laxative.

According to David Schardt senior nutritionist of the Center for Science in the Public Interest, “This suggests that the problems are widespread and that quality control for many companies, whether through ignorance, incompetence or dishonesty, is unacceptable.”

But this goes beyond false advertising.  Herbal supplements can cause real health damage.  In 2012, the FDA blamed them for causing over 50,000 adverse events annually. Some pills use fillers that are made up of rice, or worse, black walnut, which can severely affect those with nut allergies, while others contain unlabeled toxic ingredients.  Many also interact with prescription drugs, like garlic and ginkgo biloba which can potentiate the effect of blood thinners and cause life-threatening bleeding.

Furthermore, data presented in early November at the American Association for the Study of Liver Diseases meeting found that liver failure caused by herbal supplements, especially those used in bodybuilding, increased almost three-fold from 2004 through 2012.

Despite the data, many patients I see in my clinic feel that supplements are safe, sometimes even preferring them to prescription drugs.  This reflects the mindset of the majority of Americans who falsely believe that herbal pills have to be FDA-approved before sold.  Patients also may not be aware that up to 70% of herbal drug producers violated manufacturing guidelines designed to prevent adulteration of their pills.

Of course, prescription medications have the potential of uncommon, and in rare cases, serious, side effects.  But these drugs are regulated by the FDA, so at least we know what’s inside them, and what’s inside them works.  That’s certainly far more than we can say about the vast majority of herbal supplements patients take today.

Kevin Pho is an internal medicine physician and co-author of Establishing, Managing, and Protecting Your Online Reputation: A Social Media Guide for Physicians and Medical Practices. He is on the editorial board of contributors, USA Today, and is founder and editor, KevinMD.com, also on Facebook, Twitter, and LinkedIn.