Are the foods you eat and supplements you take making your medications less effective?

Grapefruit for breakfast might have just sabotaged your medication. The green tea you’re sipping could be canceling out the effects of your cancer treatment. The St. John’s wort you take for mood support may be making your birth control ineffective. The foods and supplements we reach for to stay healthy can sometimes do exactly the opposite when mixed with prescription drugs.

While three-quarters of Americans use dietary supplements, and nearly two-thirds are on prescription drugs, millions are unknowingly combining substances that shouldn’t mix.

More than 85 medications can dangerously interact with grapefruit alone. Some interactions weaken your medicine, rendering treatments useless. Others amplify drug effects, turning safe doses into dangerous ones.

“All medicine is three parts poison; if it has no poison, it is not medicine,” Dr. Yen-Nien (Jason) Hou, coordinator of the Herb Information Center at Memorial Sloan Kettering Cancer Center and a pharmacist and traditional Chinese medicine herbalist, told The Epoch Times. “This means that any remedy potent enough to heal can also cause harm if used incorrectly, in excess, or in the wrong setting.”

How Supplements, Herbs, and Foods Hijack Medications

Supplement and medication interactions start in your gut and liver, where “worker proteins” – enzymes such as CYP3A4 – and “pumps” – such as P-glycoproteinvprocess medications, Hou said.

Some herbs and foods turn these workers up, clearing drugs from your body too quickly and reducing their effectiveness. Others slow them down, causing drugs to build up to dangerous levels and increasing side effects. Others interact directly with medications – thinning blood, stimulating the immune system, or blocking absorption.

Because interactions are varied and complex, if you’re on medications, always consult a qualified herbalist, pharmacist, or physician before taking supplements or herbs, and ask about any interactions, including foods that may affect their potency.

St. John’s Wort: The Saboteur

St. John’s wort has been used for centuries to treat symptoms ranging from nervous tension to intestinal colic. Today, the herb has become a common natural remedy for mild to moderate depression, anxiety, stress relief, mild insomnia, and the symptoms of menopause. It is also used topically for wounds and to alleviate nerve pain.

St. John’s wort can make many drugs less effective. It contains compounds that activate certain enzymes and drug transporters in the body.

It speeds up the breakdown of CYP3A4, an enzyme in the liver and gut. It also activates P-glycoprotein (P-gp), a pump that pushes drugs out of your cells, Hou said. When these are switched on, your body clears medications more quickly than usual, meaning fewer of them reach your bloodstream and their effects are weakened.

Affected drugs include some oral chemotherapy drugs, immunosuppressants, and birth control pills. Clinically significant interactions have also occurred when combining St. John’s Wort with benzodiazepines, used to treat anxiety and insomnia, and heart medications such as warfarin and digoxin, according to Hou.

Be sure to speak to a trusted health care provider if you are on medication and would like to take St. John’s wort.

Grapefruit: The Double-Edged Fruit

Grapefruit can make some drugs dangerously strong and others ineffectively weak.

Grapefruit slows intestinal CYP3A4, which raises levels of many oral drugs, including some cancer medications, Hou said. Grapefruit contains naringin, bergamottin, and dihydroxybergamottin, all of which can slow or shut down CYP3A4 in the gut. The effect can last from hours to a full day after consumption, meaning even your morning grapefruit can affect an evening medication.

Grapefruit can make drugs less effective. For instance, grapefruit reduces the absorption of fexofenadine, decreasing how well the drug works. Allegra is the brand name for fexofenadine, which relieves seasonal allergy symptoms. It is available as a prescription and over the counter. Its label says not take it with fruit juices, as it may not work as well even when taken with apple or orange juice, according to the FDA.

There are also an increasing number of drugs with the potential to interact with grapefruit. A study published in CMAJ found that grapefruit interactions occur only with orally administered medications, as they are metabolized in the intestines.​

Not everyone has the same amount of CYP3A4 enzyme, so grapefruit affects people differently, even when taking identical medications. Seniors are particularly vulnerable to adverse reactions.

Ginkgo Biloba: The Bleeding Risk

Ginkgo biloba is one of the most commonly used herbs worldwide. The leaf is the part used medicinally and is among the most studied herbal medicines. Most scientific research uses a proprietary, standardized extract (EGb 761) made using the leaves, which are high in flavonoids.

People take ginkgo to improve memory and cognitive function, for issues with blood flow, as well as anxiety and depression, due to its ability to increase blood flow and protect nervous tissue. Ginkgo also has antioxidant and anti-inflammatory effects.

Ginkgo can increase bleeding risk, especially when taken with blood thinners like warfarin, Hou said.

Other types of drugs that can increase the risk of bleeding include prescription blood thinners such as Eliquis and Plavix, nonsteroidal anti-inflammatory drugs such as Advil and Motrin, selective serotonin reuptake inhibitors such as Prozac and Zoloft, and serotonin-norepinephrine reuptake inhibitors such as Cymbalta and Effexor.

Some foods also have blood-thinning effects, such as garlic and ginseng. While amounts in foods are usually not problematic, taking high or concentrated supplemental doses, such as those measured in grams or hundreds of milligrams, should be avoided, especially for those on blood-thinning medications.

Because ginkgo can thin the blood, you also want to make sure that you don’t take it before going into surgery, Feather Jones, a 30-year clinical herbalist and educator in Sedona, Arizona, told The Epoch Times.

Several other types of drugs have possible interactions with ginkgo biloba, and include:

* Acid-reducing drugs

* Oral diabetes drugs

* Procardia (Nifedipine): a calcium-channel blocker used to treat some heart conditions

* Xanax (alprazolam): used for panic attacks and anxiety

* Statins: used to lower cholesterol levels

* Anti-seizure medications

Check with your health care team before you start taking ginkgo biloba to ensure there are no interactions with your medications and that it can be added safely.

Green Tea: When Healthy Becomes Harmful

Green tea is one of the most popular beverages in the world, known for its abundant antioxidants that support heart health, boost brain function, aid in weight management, and potentially reduce the risk of certain cancers.

Green tea contains a powerful polyphenol called EGCG (Epigallocatechin gallate), which is responsible for many of its health benefits. However, it can significantly interact with and even completely negate the anticancer effects of the drug bortezomib (Velcade), a proteasome inhibitor used to treat multiple myeloma, a blood cancer, and glioblastoma, a very aggressive brain cancer.

Hou said that laboratory data have shown potential interference. “Although later data suggest that typical dietary amounts may be okay, so we individualize advice.”

Interactions have also been reported between green tea and other drugs:

* Statins for lowering cholesterol

* Some blood pressure medicines

* Warfarin: an anticoagulant used to prevent blood clots

* Some medications that treat the symptoms of menopause

Dried green tea leaves also contain vitamin K, and excess amounts can increase blood clotting. If you are on blood thinners, be aware of the risk and talk to your doctor about whether you should limit the amount of green tea you drink.

Final Thoughts

Navigating the world of drug interactions can seem overwhelming, but keeping communication channels open is a good first step.

“I always encourage my clients to communicate with their doctor on what they have decided to do and not to be strong-armed into believing something without doing diligence – without speaking or doing their homework,” Jones said.

She encourages clients to share what was discussed in their sessions with their doctors. An open dialogue allows doctors to work with patients and their treatments, rather than against them.

For Hou and his team at Memorial Sloan Kettering Cancer Center, transparency is critical to optimal patient care. During the initial patient interview, he said that patients are asked why they are using each herb or supplement and what they hope to achieve, which helps him and his team provide the best clinical evidence for their safe use.

Remember Hou’s ancient wisdom: Any remedy potent enough to heal can also cause harm if used incorrectly. The goal is not to avoid healthy foods but to balance benefits and risks with knowledge and professional guidance.

Written by Emma Suttie for Epoch Health ~ January 20, 2026