Common Herbs That Can Interfere With Prescription Drugs

Herbs and medications can complement each other when used with expert guidance.

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Most of Feather Jones’s clients are taking pharmaceuticals, but they don’t want to be. They come to her, a clinical herbalist, to get off whatever drugs they can, and to manage the side effects of the ones they can’t. It’s a meticulous process that takes time and skill.

“When I look at the list of their current meds, I have to look and see what they’re doing to make sure that what I’m recommending doesn’t nullify what the drug is attempting to do, or over-enhance it,” she told The Epoch Times.

It’s a calculation that matters more than ever as an increasing number of people taking prescription medications turn to herbal supplements—often without professional guidance and sometimes without telling their doctors.

How Herbs Interfere With Medications

The interactions between herbs and drugs occur through several mechanisms, some of which are surprising in their specificity and potency.

Herbs Change How the Liver Processes Medications

More than 50 percent of medications are broken down by CYP450 enzymes, primarily in the liver but also in the small intestine. Some herbs can speed up or slow down these enzymes, affecting how much medication remains active in the system—either too much or too little.

When CYP enzymes are inhibited by substances such as grapefruit, goldenseal, some antibiotics, and antifungals, drug levels in the bloodstream rise, increasing the risk of side effects and toxicity.

When enzymes are activated by inducers such as St. John’s wort, certain antibiotics, and anticonvulsants, medications are cleared from the body too quickly, leading to reduced effectiveness.

St. John’s wort can make antidepressants, birth control pills, blood thinners, heart medications, and some cancer drugs less effective.

Herbs Thin the Blood or Affect Clotting

For anyone taking blood-thinning medications such as warfarin, aspirin, nonsteroidal anti-inflammatory drugs, and anticoagulants such as Eliquis, Pradaxa, and Xarelto, certain herbs create significant bleeding risks.

Certain herbs increase the risk of bleeding by reducing platelets’ ability to stick together, such as garlic, ginkgo, ginger, turmeric (curcumin), and feverfew. When one takes these and pharmaceutical blood thinners, small cuts can bleed longer, one may bruise more easily, and the risk of bleeding during surgery is increased.

Other herbs contain coumarins, which block vitamin K’s ability to help blood clot, such as chamomile, fenugreek, and red clover.

A third category of herbs has both antiplatelet and anticoagulant properties and increases bleeding via both mechanisms. Examples are dong quai and evening primrose.

Most herbs don’t cause bleeding on their own, but the risk increases when they are taken with certain medications, especially blood thinners or anticoagulants, as well as when the herbs are taken in high doses or are used after trauma or before surgical procedures.

Herbs Raise or Lower Blood Pressure

Herbs can influence blood pressure in multiple ways. They can dilate or constrict vessels, alter fluid balance, change heart rate, affect the nervous system, or change levels of regulatory hormones. For anyone taking medications for high blood pressure, these effects can either counteract treatment or dangerously amplify it.

Some herbs that increase blood pressure are:

• Ephedra (Ma-huang): Can cause severe high blood pressure, especially when combined with stimulants, such as caffeine and monoamine oxidase inhibitors prescribed for depression. The sale of ephedra was banned by the U.S. Food and Drug Administration in 2004.
• Licorice: Contains glycyrrhizin, which affects electrolyte balance and can increase blood volume and pressure, an effect that is intensified when licorice is combined with antihypertensive drugs.
• Guarana: Contains high levels of caffeine, theophylline, and theobromine, stimulants that affect the heart and central nervous system and can raise blood pressure.
• Bitter Orange: Contains a stimulant called p-synephrine, which is similar to ephedrine. Studies suggest that prolonged use can significantly increase both systolic and diastolic blood pressure.
• St. John’s Wort: Can raise blood pressure, especially when combined with medications that increase serotonin levels, such as many antidepressants.

On the opposite end of the spectrum, many herbs can help lower blood pressure naturally. However, when combined with blood pressure medications, they can lower blood pressure too much and cause dangerous symptoms such as weakness, dizziness, and blurred vision. Examples include garlic and ginger, hawthorn, green tea when taken in concentrated form, and danshen, a traditional Chinese herb with a wide range of applications, commonly used to improve blood circulation.

Herbs Affect Mood-Related Medications

Herbs can affect mood medications by altering drug metabolism, changing the drug’s effects, and affecting transporters such as P-glycoprotein, which pushes drugs out of cells.

Ginkgo biloba can inhibit liver enzymes and can increase levels of antipsychotic drugs such as risperidone, used to treat schizophrenia, bipolar I disorder, and symptoms of irritability in children with autism.

Herbs such as St. John’s wort, ginseng, and nutmeg can affect levels of neurotransmitters, including serotonin, dopamine, and norepinephrine, in the brain. When mixed with selective serotonin reuptake inhibitors (SSRIs), their use can lead to serotonin syndrome, a potentially life-threatening condition characterized by toxic levels of serotonin in the body. Symptoms range from diarrhea to seizures.

Other herbs used to treat anxiety, such as valerian and kava, can increase drowsiness and amplify the sedative effects of some medications such as benzodiazepines, sleep medications, opioids, and antidepressants such as SSRIs. The combination of herbs with sedative actions and the above-mentioned medication types can cause symptoms such as drowsiness and dizziness, as well as problems with thinking and judgment.

How to Combine Herbs and Drugs Safely

The growing prevalence of herb–drug combinations doesn’t mean they can’t work together. With proper guidance and precautions, many people successfully integrate both approaches.

Work With Knowledgeable Professionals

Herbs and medications can be used harmoniously, but perhaps the most important factor is using them under the guidance of a knowledgeable professional who can help you navigate potential side effects. Clinical herbalists can assist you in safely adding herbs and advise on interactions. Also, Western practitioners are increasingly aware of the need to address herb–drug interactions.

Yen-Nien Hou is the coordinator of the Herb Information Center at Memorial Sloan Kettering Cancer Center. He is trained as a traditional Chinese medicine herbalist and Western pharmacist, and his role is to consult with patients about how herbs may interact with medications and find ways to strike a harmonious balance.

“During a patient interview or herbal consult intake, we ask why each herb or supplement is being used and what the patient hopes to achieve. This helps us provide the patient with the best available clinical evidence for their use,” he told The Epoch Times. “When evaluating herbal therapies, we focus on their impact on improving function, quality of life, and symptom management, and how they align with each patient’s goals.”

Dosage Matters

Unlike pharmaceuticals, which are standardized and prescribed based on age, weight, and general health status, herbal products vary in strength and quality. Different preparation methods also deliver different dosages.

A cup of herbal tea is often mild and well-tolerated, making it a good way to introduce an herb to see how you feel. A tincture—a concentrated herbal preparation preserved in a solvent such as alcohol—delivers stronger effects. Capsules and tablets purchased from reputable sellers deliver some of the most potent, standardized doses of an herb.

A good rule of thumb when adding a new herb is to start with low doses and increase slowly so you can track how you feel.

Another factor is understanding that herbs work differently from medications and are often not taken long-term.

“We explain that herbal medicine works to correct imbalances in the body; once balance is restored, there is often no need to continue the herbal regimen,” Hou said. “For example, an herbal formula for constipation may regulate bowel movements, but overuse could disrupt the system in the opposite direction, leading to bloating or loose stools.”

He cautions against the “more is better” mentality and the idea that if the body is “deficient” in a certain herb, that deficiency can be harmful.

“Large doses may stress the liver and kidneys as they work to clear excess compounds from the body,” he added.

‘Natural’ Does Not Mean ‘No Side Effects’

People often assume herbs are universally gentle. Many are, but some have powerful effects on our bodies and minds, which is why they have been the main source of medicine for most of human history. In untrained hands, herbs can cause unwanted problems, especially when combined with medications.

Keep a List of Everything You Take

One of the most proactive steps you can take if you are on medications or any other health products is to make a list. This simple tool can help you keep track of medications, their amounts, and why you are taking them. It can also ensure everyone on your health care team is aware of everything you are taking, stays informed of any changes, and can reference your list for possible interactions.

When creating your list, be specific. Add your name, age, and weight, as well as any conditions that have been diagnosed. If possible, break the products you take into categories such as pharmaceuticals, over-the-counter medications, vitamins, herbs, and supplements to help you stay organized and make updates easier.

A list becomes especially valuable for older adults who are particularly vulnerable to drug interactions and more often use more than five different medications at once. A complete list can reduce the risk of unwanted consequences and even save someone’s life in the event of a serious interaction, accident, or loss of consciousness.

Always Keep Communication Channels Open Between Providers

A vital strategy for mitigating the effects of interactions and ensuring you combine medications and herbs wisely is to keep the lines of communication open among all members of your health care team. This includes, but is not limited to, physicians, specialists, herbalists, naturopaths, and practitioners of Chinese medicine.

Medications and herbs can work together and even complement each other when their use is overseen by skilled practitioners. As Hou has experienced with his work at the Herb Information Center, many patients benefit from the combination.

One of Hou’s patients successfully used herbal therapy to manage the side effects of her cancer medications. She continues to enjoy a good quality of life and remains disease-free.

“The patient’s ongoing well-being highlights the positive impact of a carefully managed integrative approach,” Hou said. “We continue regular follow-ups, especially around herbal medicine refills, to support the patient’s health and maintain wellness.”

Note: While the potential for herb–drug interactions is increasing, the vast majority of dangerous interactions involve medications or drug-to-drug interactions, which result in millions of emergency room visits and hospitalizations in the United States per year. A 2025 analysis estimates the number of deaths from adverse drug events in the United States to be in the hundreds of thousands annually.