Dear Dr. Blonz: At times during the previous year, I took St. John’s wort for periodic bouts of mild depression. I have had little success with the prescription antidepressants I have tried. Does the fact that I have not had any problems with my St. John’s wort indicate that I can continue taking it? — S.C., Tulsa, Oklahoma

Dear S.C.: We all need to appreciate that the human body has sophisticated systems designed to protect it from potential dangers posed by unfamiliar substances. These systems try to detoxify, break down or eliminate “foreign” compounds that enter the body. Foreign compounds can include everything from herbal products and prescription or over-the-counter (OTC) drugs to pesticides and environmental pollutants. It doesn’t matter that some of these might be thought of as beneficial; foreign compounds get identified as such and processed for elimination.

The complexity starts because there can be multiple compounds processed at any given time. This gives rise to interactions between medications and herbs that can affect the way they work and the rate they get eliminated from the body. Our liver is the focus of this process. The method typically involves a reaction with the substance that’s tantamount to putting metabolic handcuffs on it, preventing it from being active while it’s in queue for elimination.

A specific family of enzymes plays a key role in metabolizing, or breaking down, unknown substances. Compounds broken down via this enzymatic system include herbs; drugs used to treat heart disease, HIV infections, seizures, depression and cancer; drugs used to prevent the rejection of transplanted organs; and oral contraceptives. Different substances can either compete with each other for enzyme attention — resulting in slower decreases in their respective blood levels — or they can stimulate the enzymes, which results in a more rapid decline. This is significant for health conditions where reliable medication blood levels are a key part of the treatment.

St. John’s wort is metabolized by this enzyme system, and it acts as a stimulant. That means that if St. John’s wort is being taken, the blood levels of other drugs can be lower than expected — lower, even, than needed to achieve that drug’s therapeutic effect.

I don’t know if you are taking other medications or substances, but this is definitely a discussion you should have with your physician or pharmacist without delay.

Before prescription drugs are approved by the Food and Drug Administration, they have to undergo rigorous testing for safety and efficacy. Tests are also done to determine how a drug works, the effective dose, any potential side effects or adverse reactions, how long the drug lasts, and how it is eventually eliminated from the body. All this helps to provide the information used by health professionals when dispensing the drugs. For OTC drugs, this info is available for you either on the package or in the package insert.

Herbs have been in use for centuries, and some may have health-boosting potential. Our knowledge, however, about side effects and interactions with other medications — even with other herbs — is still in its infancy. That is one of the reasons why people should approach the use of herbs with caution, especially when also using other medications. There are websites providing interaction information, including drugs.com and rxlist.com, but these should not be considered a substitute for that talk with your health professional.


(Ed Blonz, Ph.D., is a nutrition scientist and an assistant clinical professor at the University of California, San Francisco. He is the author of the digital book “The Wellness Supermarket Buying Guide” (2012), which is also available as a free digital resource at blonz.com/guide.)

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.