Show 1343: Hidden Harms of Herb-Drug Interactions

Millions of Americans take dietary supplements and most of us assume they are safe. While this is probably a reasonable rule of thumb, there are some situations that require extra vigilance. In particular, we must be careful of interactions between herbs and drugs. Even your doctor may not be aware of the hidden damage.

How risky are herb-drug interactions?

It’s easy to compartmentalize drugs in the pillbox, herbs in the bottle. Even though we think we can easily distinguish between drugs and natural products, our bodies can’t. Our cells use the same machinery (mainly enzymes) to handle everything we take in, including food, herbs, and medications. Some herbs, such as St. John’s Wort (Hypericum perforated), have profound effects on these enzymes. This, in turn, can change the way our bodies handle the medications we may be taking. Could taking St. John’s Wort to relieve depressed mood make birth control pills lose their effectiveness?

Waking up with grapefruit:

The tart taste of grapefruit juice is definitely a wonderful way to wake up sleepy taste buds in the morning. But we’re talking about a different kind of wake-up call here. In 1991, scientists published a study with some surprising results. Grapefruit juice used to mask the taste of alcohol significantly increased blood levels of the blood pressure pill felodipine (Hand, February 2, 1991). This was enough to produce unpleasant symptoms such as hot flashes and dizziness. Orange juice did not produce the same effects.

Why was that a wake-up call? First of all, it was the first report of grapefruit influencing medications. There is now a significant list of drugs that interact with grapefruit. High blood levels of these medicines can make side effects more likely.

Second, the prominence of grapefruit interactions with felodipine, simvastatin, and other common drugs alerted us to the possibility of herb-drug interactions. These aren’t always widely advertised, though. How can you protect yourself from hidden damage

Know the interactions between herbs and drugs:

If you’re taking herbal supplements and pharmaceuticals, ask your pharmacist to help you check for potential interactions. The National Center for Complementary and Integrative Health (NCCIH) website has some information that may be helpful. Also, your pharmacist should have access to the Natural Medicines Database, a great resource on this topic. Other online resources such as WebMD or can also guide you to the information.

One problem is that scientists haven’t thoroughly studied the interactions between herbs and drugs. Some of the warnings you may find online may be based on test-tube studies which don’t always translate well to human bodies. For example, some sites warn that ginkgo and ginseng interact with numerous medications. In practice, however, integrative health practitioners rarely see any hidden harms associated with these herbs.

However, there are other herbs that can interact with medications. Goldenseal and the berberine compound it contains can interact with several drugs, including aromatase inhibitors, statins, metformin, and anti-androgens (Scientific reportsJune 16, 2016).

Interactions between drugs and nutrients:

Herb-drug interactions aren’t the only possible sources of hidden harm. Some medicines may increase nutritional requirements. For example, the diabetes drug metformin can lead to low vitamin B12 levels over time. People taking this drug for an extended period should have their vitamin B12 levels tested annually. They may need to take supplements.

Another nutrient interaction appears with blood pressure pills known as ACE inhibitors or ARBs. These can reduce levels of zinc, a mineral crucial for proper immune function. Testing for zinc is difficult and doctors don’t do it often.

Discuss herb-drug interactions with your healthcare partner:

Some people are reluctant to tell their doctor or PA that they are taking herbal supplements. They fear that the supplier will scold or make fun of them. But to protect yourself from the hidden harms of herb-drug interactions, it’s essential to talk about what you’re taking and why. You may be able to adjust your drug regimen or herbal supplements.

This week’s guests:

D. Craig Hopp, Ph.D., is assistant director of the Division of Extramural Research at the National Center for Complementary and Integrative Health (NCCIH). In addition to serving as Deputy Director, Dr. Hopp continues to oversee the administration’s product integrity policy. This involves evaluating proposed study materials to ensure they are safe and adequately characterized. He also focuses on large-scale projects such as Natural Product Drug Interaction Research, the Research Center for Innovation and Technology, and the Consortium for Advancing Research on Botanical and Other Natural Products (CARBON) program. Hopp uses his expertise and experience in the natural products field to help set research priorities at NCCIH.

Dr. Hopp’s photo is by Lisa Helfert.

Craig Hopp talks about natural remedies

Craig Hopp, PhD

Dr. Tieraona Low Dog is a founding member of the American Board of Physician Specialties, the American Board of Integrative Medicine and the Academy of Women’s Health. She was elected chair of the US Pharmacopeia Nutritional Supplements/Botanical Expert Committee and was appointed to the Scientific Advisory Board of the National Center for Complementary and Alternative Medicine. Her books include:Women’s health in complementary and integrative medicine; Life is your best medicine AND Fortify Your Life: Your Guide to Vitamins, Minerals & More. His website is

Dr. Tieraona Low Dog describes natural ways to treat heartburn

Dr. Tieraona Low Dog describes natural ways to treat heartburn

Listen to the podcast:

The podcast for this show will be available on Monday, June 12, 2023, following its broadcast on June 10. You can stream the show from this site and download the podcast for free.

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