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Herbal Medicines and Prescription Drug Interactions

Many popular herbal medicines have prescription drug interactions. Learn about them before including both herbs and drugs in your regimen.

Each day more and more people are taking herbs and botanical products to help them with a variety of disorders. The effectiveness of these supplements can vary by condition and individual, but one fact is clear: these supplements can have interactions with prescription drugs, over-the-counter drugs, dietary supplements, and even elements in our food.

According to the National Institutes of Health (NIH), herbal medicines can pose similar dangers as other pharmaceuticals. Too often, people who are taking supplements don’t recognize these interactions until it is too late.

Does “All-Natural” Always Mean Safe?

Not always. Although supplements might be benign on their own, many people taking them are in the dark about the potential hazards of their interactions with other substances. People should always do their own research, as well as speak with their doctor or pharmacist. However, many people skip this step.

To make matters worse, the NIH notes that research into herb-drug interactions is lacking. They point out most identified interactions are hypothetical, and are based mostly on indirect observations, such as animal studies or cellular assays. It’s even more prudent, then, to be cautious in mixing supplements with prescription drugs, and to encourage further research into both the benefits and risks of herbal medicine.

Below are some interactions that people should know about before combining natural remedies with prescription medications.

How Do I Handle a Drug Interaction?

The first best step is to consult with your doctor and pharmacist before taking about medication, herbal, prescription, or otherwise. While research is beginning to show the benefits of many herbal or other natural supplements, we are still in the dark about long-term effects and the interactions many of these medicines have both with each other and with prescription drugs.

It’s important to understand that herbal medicines can have synergistic effects with pharmaceutical drugs. Synergy is when two substances or compounds interact in a way that combines their separate effects into a stronger effect. In other words, their sum becomes greater than the individual parts.

This can be great news as researchers uncover more effective treatments for diseases and illnesses, but this same synergy can apply to negative effects.

Please do not stop taking your medication unless you have been told to do so by your doctor. With the help of your doctor and pharmacist, you can determine which interactions might be insignificant and which could be serious.

Here are some common herbal supplements and potential prescription drug interactions.

Black Cohosh:

Black cohosh is a plant that grows in North America. Women often take black cohosh for menopausal disorders (such as “hot flashes”), painful menstruation, vaginitis, and uterine spasms. One issue to be aware of is that prescription drugs that are broken down by liver enzymes might accumulate in the body and eventually become toxic if taken with black cohosh. Some researchers are also concerned that black cohosh could also be toxic to the liver or might enhance liver toxicity when interacting with medicine such as atorvastatin (Lipitor), acetaminophen (Tylenol) or even alcohol.

Coenzyme Q10:

CoenzymeQ10 is known just as often as “ubiquinone” or CoQ10. It’s found naturally in organs such as the heart, kidneys, pancreas, and liver. Aging, along with smoking, can lessen the amount of CoQ10 our bodies produce.

CoenzymeQ10 is touted to help repair heart damage caused by some cancer medications as well as for gum disease, breast cancer, or muscular dystrophy.

People taking anticoagulant drugs such as warfarin (Coumadin) should be aware that CoenzymeQ10 may decrease the blood thinning effects of these anticoagulants, which may increase the risk for a blood clot. Patients may need their blood clotting tests checked more often and may need to change their anticoagulant dose.


One would think that a supplement as natural and benign sounding as cranberry would have no drug interactions, but cranberries and cranberry-based supplements have a number of interactions.

To begin with, cranberries naturally are high in vitamin C, and many patients drink cranberry juice to ward off urinary tract infections (UTIs) – although the evidence is still unclear on how well, if at all, cranberry prevents UTIs.

Patients should be aware that cranberry might increase the efficacy of anticoagulants (also known as blood thinners) such as warfarin and lead to bleeding or bruising. People with prescriptions for anticoagulants should check with their doctor before consuming large amounts of cranberry or drinking large amounts of cranberry juice. This might require that their International Normalized Ratio (INR) or other blood clotting lab test be checked more frequently.


Also known as Purple Coneflower or American Coneflower, Echinacea is used to stimulate the immune system. It is commonly used to help treat the common cold.

Echinacea is thought to slow the breakdown of caffeine in your body, so, when taken with caffeine, it may increase side effects such as jitteriness, headache, or insomnia.

Echinacea can also affect how your body metabolizes some drugs that go through your liver. These interactions can be complicated, so always check with your doctor and pharmacist.


Feverfew is a plant traditionally used for the treatment of fevers, rheumatoid arthritis, migraine headaches, and problems with menstruation.

Feverfew might increase the risk of bleeding when used in conjunction with blood thinners such as heparin, warfarin, Pradaxa (dabigatran), Xarelto (rivaroxaban), Plavix (clopidogrel), and aspirin.

Consult with your doctor and pharmacist before using feverfew.


Ginger is most commonly considered a flavoring agent or food product, but it is also used as an herbal supplement. Ginger has been used to prevent motion sickness and vertigo, as well as reduce stomach acidity and increase appetite.

Ginger does not have a clear and thorough list of prescription drug interactions, although it is known to inhibit thromboxane synthetase, which can prolong bleeding time and may cause interactions with anticoagulants like warfarin, aspirin, and other blood thinners.

Consult with your doctor and pharmacist before taking ginger supplements.

Ginkgo Biloba:

Ginkgo is used to treat symptoms of Parkinson’s disease and Alzheimer’s, as well as to help with general memory support.

Ginkgo has hundreds of potential drug interactions. Along with possibly decreasing the antiviral effects of drugs used in the treatment of HIV (e.g. efavirenz and indinavir), it can also alter the actions of medicines that are metabolized through the liver. The list of potential interactions is extensive, and includes common medications like omeprazole (Prilosec OTC), fluvastatin (Lescol), and donepezil (Aricept). Patients who take seizure medications, blood thinners or diabetes drugs should also avoid ginkgo.


Ginseng is used for a variety of purposes, including to increase vitality and improve a person’s resistance to stress.

Ginseng has many types of drug interactions. Long-term use of ginseng might lead to a decrease the effectiveness of blood thinners and anticoagulants such as warfarin, and therefore increase the risk of developing blood clots. Ginseng can also interact with blood pressure and diabetic medications like insulin or oral hypoglycemics. Be sure to check with your doctor and pharmacist or doctor if you use ginseng.


Goldenseal is an herb that traditionally grows in the northeast United States. People use goldenseal for skin infections, for cold and flu symptoms, and to treat diarrhea. There are dozens of potential drug interactions with goldenseal.

Goldenseal can have serious interactions with certain antipsychotic drugs. As an example, using goldenseal with pimozide or thioridazine is not recommended, as it may lead to an irregular heart rhythm.

Always check with your doctor and pharmacist to be sure goldenseal will not interact with your prescription medicine, over-the-counter medicine, or other herbal supplements.

Green Tea:

Most of us think of green tea as a popular drink, but it has also been promoted for the treatment of stomach disorders, to lower cholesterol, as an anti-cancer antioxidant, among many other uses. Green tea consumption – as a drink and supplement – has recently gained popularity due to many claims that it will boost metabolism and reduce inflammation.

Dried green tea leaves contain vitamin K, which may increase blood clotting. Large amounts of vitamin K might interfere with the efficacy of blood thinners. Large amounts of green tea (one-half to one gallon daily) may be enough to cause a substantial decrease in the INR (a measure of blood clotting) in patients being treated with warfarin. Patients using warfarin should avoid large amounts of green tea since it may interfere with the medication’s blood-thinning capabilities.

Green tea, either as a beverage or as extract, can reduce blood levels of the blood pressure medicine nadolol (European Journal of Clinical Pharmacology, June 2018).


The kava plant is a part of the pepper family. Kava is often taken to reduce anxiety and improve sleep.

There are many drug interactions with kava. To start, using kava in conjunction with medications like Buprenex, Butrans, or Probuphine can lead to serious side effects such as respiratory distress and even coma. Kava also should not be taken in conjunction with alcohol, recreational drugs, or herbs that are known to cause liver toxicity.

Consult your doctor and pharmacist before taking kava. And if you take kava, call your doctor immediately if you develop symptoms such as joint pain, fever, bleeding, appetite loss, , stomach pain, nausea, vomiting, dark colored urine, light colored stools, and yellowing of the skin or eyes – these could be markers of liver toxicity.


Melatonin is a natural hormone and is used to help regulate one’s sleeping cycle. Melatonin tablets help some people with insomnia, as well as the sleep disorders often associated with shift work or jet lag.

Since melatonin can often causes drowsiness, you should avoid taking it with alcohol and in conjunction with other medicine designed to sedate people, such as muscle relaxers, opioid analgesics, some antihistamines, as well as benzodiazepine sedatives and hypnotics. Users should also be aware of its interactions with other herbal supplements that may also cause drowsiness, such as 5-HTP, St. John’s Wort, and kava. Melatonin can also increase blood sugar, which could interfere with diabetes medications. Also, it may affect blood clotting in some people, so it should be avoided by people taking anticoagulants.

St. John’s Wort:

St. John’s wort is often used for depression. Consumers should be aware that prescription drug interactions with St. John’s wort are numerous and can be dangerous.

You should always consult with your doctor and pharmacist before using St. John’s wort. You should not combine St. John’s wort with many medications, including (but not limited to) tricyclic antidepressants (TCAs), monoamine oxidase (MAO) Inhibitors, selective serotonin reuptake inhibitors (SSRIs), warfarin, dextromethorphan, birth control pills, nefazodone, certain HIV medications, and triptans for migraine. You should even discuss interactions with your doctor or pharmacist if you take OTC, vitamin or other herbal medications.

Saw Palmetto:

Saw palmetto is a popular herbal supplement for treating benign prostatic hypertrophy (BPH), a noncancerous enlargement of the prostate gland. You should avoid taking saw palmetto in conjunction with other agents commonly used to treat BPH (unless directed to do so by your doctor).

Saw palmetto is suspected to also slow blood clotting, which could raise the risk for bruising or bleeding (particularly when used in conjunction with blood thinners, such as warfarin). Also, when saw palmetto is used in conjunction with estrogens or oral contraceptives, it could reduce the effectiveness of these hormonal therapies.


Valerian is sometime used to combat anxiety and insomnia. We’ve counted more than 500 potential prescription drug interactions with valerian, so consult with your doctor before combining valerian with sleep or anxiety medicines, muscle relaxants, antidepressants, pain killers, or any medicine that might cause drowsiness.


Yohimbe is the name given to an evergreen tree that is generally found in African countries. Yohimbe bark contains a chemical called yohimbine, which can dilate blood vessels. It is often used for erectile dysfunction or sexual problems associated with selective serotonin reuptake inhibitors (SSRIs).

Yohimbine has many interactions. It is not recommended in patients with hypertension, angina pectoris, or heart disease because it can lead to high blood pressure and a faster heart rate. Please consult with your doctor and pharmacist before taking Yohimbe.

The Future of Herb-Drug Safety:

While we are learning more each day about herbal remedies, their benefits, and their interactions, the truth is we still have a lot to uncover. While there are potentially positive effects of herbal medicines, until we have a more robust understanding, it’s important to be cautious. In this regard, always have a conversation with your doctor or your pharmacist about any herbal medicines you plan to take or are currently taking.

In addition, communicate any changes in side effects to your doctor immediately. For further information on drug-herb interactions, the NIH provides a dietary supplement fact sheet that can be helpful in learning more about possible interactions and side effects of herbal supplements.

Author Biography:

Jeremy Lee currently serves as the Director of Drug Information for America’s Pharmacy – a prescription discount program accepted in pharmacies across the United States. Jeremy graduated from UCLA with a degree in biology and went on to receive his PharmD from the University of California, San Francisco. He has over 20 years of experience in the pharmaceutical industry.

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About the Author
Jeremy Lee, PharmD, BCPS, currently serves as the Director of Drug Information for America’s Pharmacy – a prescription discount program accepted in pharmacies across the United States. Jeremy graduated from UCLA with a degree in biology and went on to receive his PharmD from the University of California, San Francisco. He has over 20 years of experience in the pharmaceutical industry..
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