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18 Herbal Supplements with Risky Drug Interactions

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on July 26, 2020.

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What is an Herbal Supplement?

The use of herbal supplements has a long history - dating back thousands of years. Examples of important medicines extracted from botanicals include reserpine, morphine, penicillin, and vinca alkaloid anti-cancer drugs.

Today, herbal supplements and nutraceuticals can be purchased over-the-counter (OTC) and may be labeled "all-natural". Herbal supplements are sold in many different forms - dried leaves for teas, powdered, as capsules or tablets, or in solution.

But does "all-natural" mean they are always safe?

No. While these products are intended to boost health, and may make claims to that effect, robust clinical studies may be lacking. It's important to discuss supplement use with your doctor. Drug interactions with herbs can be especially risky.

Does the FDA Regulate Herbal Products?

The FDA does not apply the same effectiveness and safety studies used for prescription drugs to herbals, dietary supplements, and their manufacturers. The FDA can and does seize and remove from the market tainted, contaminated or unsafe dietary supplements when they are aware of problems; kratom is one example that has been involved in many seizures.

Learn More: What is Kratom?

Herbal supplements are not subject to review by the FDA and their use can often be risky.

  • Consumers need to understand that even though the label may say "natural", these products are not always safe, as demonstrated by "all natural" alternatives for erectile dysfunction that the FDA found contained actual prescription medications.

Aren't Herbs Are 'All Natural' and Safe?

Even though herbal supplements may be from plant or herb sources, the active ingredients can still be potent chemicals. Because of this, herbal supplements can have drug interactions, even with each other or with food or alcohol. Unfortunately, these products are not labeled with safety warnings, and it is difficult for a consumer to know if an interaction may occur.

Herbal interactions with prescription medications or other chemicals can:

  • interfere with how the drug may be broken down in the body
  • enhance side effects of prescription medications
  • block the intended therapeutic effect of a drug.

You can search for herbal supplement-drug interactions here, and always check with your doctor or pharmacist for clarification.

Black Cohosh

Image Credit: Wikipedia

Black cohosh is a shrub-like plant found in North America. Black cohosh is often used for menopausal disorders ("hot flashes"), painful menstruation, uterine spasms, and vaginitis. However, prescription drugs broken down by certain liver enzymes may accumulate in the body and lead to toxicity if used with black cohosh. There is concern that black cohosh might also be toxic to the liver and may enhance liver toxicity with certain medications, such as:

Let's face it, drug interactions are complicated and numerous, so have your medications -- even herbals and OTCs -- screened by your pharmacist to review for black cohosh drug interactions, or other herb-drug interactions.

Coenzyme Q10

CoenzymeQ10, also known as ubiquinone or CoQ10, is found naturally in the heart, kidney, liver and pancrease, but aging and smoking can deplete these natural stores.

CoQ10 is promoted to help heart damage caused by certain cancer medicines and for breast cancer, gum disease, or muscular dystrophy, although robust studies confirming these uses are lacking.

However, use of CoQ10 with anticoagulant drugs like warfarin may decrease the blood thinning effects of the anticoagulant and increase the risk for a clot.

If you are considering the use of any supplement, always check with your doctor first. And if you take a blood thinner, check with your doctor before starting CoQ-10. You may need to have your blood clotting tests checked more frequently and may need a change in your anticoagulant dose.


Even the simple, delicious cranberry can have drug interactions.

  • Cranberries are a fruit chock full of vitamin C, and some people drink cranberry juice to help prevent urinary tract infections (UTI).
  • Although data is conflicting, some studies have shown cranberry can reduce recurrent UTIs in pregnant women, the elderly and hospitalized patients; but it is not helpful to cure a UTI.

Cranberry may exert an increased effect on blood thinners (anticoagulants) like warfarin and lead to bruising or bleeding. If you take an oral blood thinner, check with your doctor before consuming unusual amounts of cranberry or cranberry juice. You may need to have your International Normalized Ratio (INR) or other blood clotting lab test checked more frequently.


Echinacea is also known as the American Cone Flower, Black Susan, or Purple Coneflower. Echinacea has been used to stimulate the immune system, and is most commonly used in the treatment of the common cold.

Most echinacea drug interactions are not serious; however, it can affect blood levels of drugs like tizanidine (Zanaflex), a muscle relaxant or rasagiline (Azilect) used in Parkinspn's disease. Echinacea can slow the breakdown (metabolism) of caffeine in your body, and could lead to side effects like jitteriness, headache, or insomnia.

Echinacea may also change how the body metabolizes many drugs that go through the liver. These are somewhat complicated interactions that can lead to side effects or reduced effectiveness of your medicine, so always check with your pharmacist.

Evening Primrose Oil

Evening primrose is a flowering plant known by other names such as Oenothera biennis, scabish, or king's cureall.

Evening primrose oil provides fatty acids used by the body for growth.

  • Evening primrose oil contains gamma linoleic acid that may slow blood clotting and increase the likelihood of brusing or bleeding.
  • If you take drugs or herbs that may have blood thinner effects (for example: warfarin), check with your health care provider before using evening primrose oil.
  • Prompty report any signs of bleeding to your doctor if these agents are combined.

Use of evening primrose oil may increase the risk for seizures if you take anti-seizure medications or phenothiazine drugs, although data regarding the effect of gamma linolenic acid on seizure threshold are conflicting and limited.

You can check for other evening primrose oil drug interactions here.


Valerian has been used to treat insomnia and anxiety, although evidence is conflicting on how well it works.

Germany's Commission E, the authorities that evaluate the use of herbal products in Germany, has approved valerian as an effective mild sedative. There are over 200 possible drug interactions with valerian, so a drug interaction screen is important when using valerian.

Speak with your doctor before combining valerian with:

or other medicines that cause drowsiness. These drugs may increase drowsiness and dizziness while you are taking valerian.

St. John's Wort

St. John’s Wort is a popular herbal supplement widely used to help with symptoms of depression. Over 500 drug interactions exist with St. John's Wort and some can be dangerous. Due to the seriousness of many drug interactions, you should consult with your health care provider before using St. John's Wort.

A sampling of drugs you should not combine with St. John's Wort includes:

There are many other possible interactions. Check with your doctor or pharmacist for a drug interaction screen with St. John's Wort if you take prescription, OTC, vitamin or other herbal medications.

Saw Palmetto

Use of saw palmetto is popular for benign prostatic hypertrophy (BPH), a noncancerous prostate gland enlargement.

  • Evidence suggests that saw palmetto may be effective for mild-to-moderate BPH, but always ask your doctor for advice about this product.
  • Saw palmetto should be avoided with other agents used to treat BPH, such as finasteride (Proscar), unless okayed by your doctor.

There are over 20 listed interactions with saw palmetto, but most of these are minor interactions.

If saw palmetto is combined with estrogens or oral contraceptives, the effectiveness of the hormonal therapies could be reduced.

The tannic acid present in some herbs like saw palmetto may inhibit the absorption of iron. The administration of these herbs and iron-containing supplements should be separated by several hours.

Check with your doctor or pharmacist for a drug interaction screen.


Melatonin is a natural hormone that helps to regulate the sleep-wake cycle. For some people, melatonin tablets may be helpful for insomnia, jet lag and shift work sleep disorders.

However, because melatonin causes drowsiness, its use should be avoided with alcohol and other sedating medicines, such as:

Other herbs that can also lead to drowsiness include 5-HTP, kava, and St. John’s Wort.

As with many herbal products, blood clotting may be affected with use of melatonin with anticoagulants such as warfarin.

Related: Melatonin: Worth Losing Sleep Over?


Kava, native to the South Pacific, is a member of the pepper family. Kava has been used to improve sleep, decrease anxiety, and tame nervousness, stress, and restlessness.

Talk to your doctor before using kava. There are over 200 drug interactions with kava.

  • Kava should not be used with alcohol or other drugs or herbs that can also cause liver toxicity.
  • The use of buprenorphine (Buprenex, Butrans, Probuphine) with kava can lead to serious side effects such as respiratory distress, coma or even death.

Products containing kava may cause liver problems, and taking them with alcohol can increase the risk. Call your doctor immediately if you have fever, joint pain, bleeding, skin rash or itch, appetite loss, fatigue, nausea/vomiting, stomach pain, dark colored urine, light colored stools, and/or yellowing of the skin/eyes; these may be signs of liver toxicity.


Ginseng has been used in Asian countries for its therapeutic effects for centuries. Today, ginseng use is reported to improve the body's resistance to stress and increase vitality, among other uses.

  • There are many different origins of ginseng, and many types of drug interactions.
  • Long-term use of American ginseng may decrease the effectiveness of warfarin, a blood thinner, and increase the risk for a blood clot. In general, ginseng or ginseng-containing herbal tea should not be used with anticoagulants. Ask your doctor about this interaction.
  • Ginseng may also affect blood pressure treatments and diabetic medications like insulin or oral hypoglycemics.

Be sure to check with your pharmacist or doctor if you use ginseng as an herbal supplement. While usually well-tolerated, important drug interactions can occur.


Yohimbe is the name of an evergreen tree that is found in some African countries.

It's important at least 14 days should elapse between discontinuation of MAOI therapy, an infrequently used treatment for depression, and initiation of treatment with yohimbine.

MAOIs are typically only used when other antidepressants have proven ineffective, because they have a higher risk of drug interactions than standard antidepressants and can also have interactions with certain foods such as aged cheeses and cured meats.

Therapy with yohimbine is generally not recommended in patients with hypertension, angina, or heart disease because it has a stimulatory effect and can lead to high blood pressure and a rapid heart rate. You can check other yohimbine interactions here. Discuss the use of this supplement with your doctor to be safe.


Feverfew is a member of the daisy family. Feverfew is often used as an herbal remedy to prevent migraine headaches and associated nausea and vomiting; however, the evidence is not conclusive.

Alarmingly, feverfew may increase the risk of bleeding, especially in people with blood-clotting disorders or using blood thinners to help prevent clots, for example:

Check with your health care provider before using feverfew; you can check for other drug interactions with feverfew here.

Ginkgo Biloba

The use of ginkgo extract dates back centuries in traditional Chinese medicine.

Ginkgo interacts with over 260 drugs; have a pharmacist check for interactions before use.

Ginkgo has been used for treating anxiety, dementia, circulation problems in the legs, premenstrual sydrome, certain vision problems, dizziness), or some movement disorders. Research has shown that Ginkgo Biloba is not likely to be effective in treating heart disease.


Goldenseal is a flowering herb that grows in the northeast United States. Common uses for goldenseal include skin infections, for cold and flu symptoms, and to treat diarrhea, but evidence is weak for these uses. There are over 90 possible drug interactions with goldenseal, have your pharmacist check for drug interactions with all your medicines.

Two of the more serious interactions occur with certain antipsychotic drugs - using pimozide or thioridazine with goldenseal is not recommended, as antipsychotic blood levels may rise leading to an irregular heart rhythm.

Goldenseal may affect liver enzymes that can alter blood levels of certain drugs; always have your pharmacist run a drug interaction screen on all of your medicines, OTC drugs, or herbs.


Garlic is a commonly used - and loved - flavoring agent, food product and herbal supplement. There are many conditions garlic has been promoted for - to reduce cholesterol and triglycerides, to prevent cancer, to lower blood sugar levels, and to reduce menstrual pain, among other uses. There are over 180 drug interactions with garlic, but most are reported as minor.

  • Garlic has been reported to moderately affect blood clotting and blood sugar levels and may affect people who take blood thinning agents like aspirin, warfarin, or clopidogrel (Plavix).
  • Use of garlic supplements with HIV protease inhibitors (PI) may decrease the PI blood levels.

There are other possible garlic interactions, so be sure to review all possible drug interactions with garlic and speak with your healthcare provider.

Green Tea

Green tea is a popular drink that originated in China and has been promoted for stomach disorders, to lower cholesterol, as an anti-cancer antioxidant, as a stimulant, and to lessen belly fat, among other uses.

In the U.S., it has gained recent popularity due to claims it can boost metabolism and aid in weight loss. Only 3 minor drug interactions have been reported with green tea.

Dried green tea leaves contain vitamin K, which can increase blood clotting. Large amounts of vitamin K may interfere with the activity of some blood thinners.

A substantial decrease in the INR (a measure of blood clotting) has been reported in a patient treated with warfarin after he began consuming large quantities (1/2 to 1 gallon daily) of green tea. Patients treated with warfarin should probably avoid large amounts of green tea as it can interfere with the blood-thinning capabilities of warfarin.


Ginger is a commonly used flavoring agent, food product, and herbal supplement.

  • Ginger has been used in the treatment and prevention of motion sickness, vertigo, to increase appetite, and to reduce stomach acidity.
  • Ginger has also been used by some women under medical supervision to reduce severe nausea and vomiting in pregnancy.

Over 50 drug interactions are reported with ginger. Drug interactions with ginger are not well documented; however, it is known to inhibit thromboxane synthetase, which can prolong bleeding time and may cause interactions with anticoagulants like warfarin, aspirin, or other blood thinners.

Check other possible ginger-drug interactions here. Always check with yourt doctor or pharmacist to check for herbal and drug interactions.

How Should I Handle Possible Herbal-Drug Interactions?

It is important to remember that the best way to handle any possible drug interaction is to predict it and prevent it.

In order to do that, you need to be proactive in checking for possible drug interactions yourself in addition to asking your health care provider to screen for interactions.

Tell your doctor or pharmacist about all the medications you take, including:

Be sure a drug interaction screen is conducted by a healthcare provider each time you start or stop a medication. Consult your doctor about any symptoms you are experiencing and discuss all herbal products prior to use.

How to Handle an Herbal Drug Interaction?

Advice from your health care provider is your best option in preventing serious health effects from any drug interaction.

Remember that herbal supplements are not subject to FDA oversight and have not usually been tested in clinical studies to prove their effectiveness or safety.

Contact your health care provider if you discover that a possible drug interaction may occur between medications and herbal products that you use.

Do not stop taking your medication unless directed to do so by your doctor. The interaction may be insignificant and no change may be needed; on the other hand, the interaction could be serious and the herbal supplement may need to be discontinued.

More questions? Visit our Top 9 Ways to Prevent a Deadly Drug Interaction slideshow and join the Herbal Support Group to ask questions about drug interactions, check on the latest medical news, and provide your feedback, too.

Finished: 18 Herbal Supplements with Risky Drug Interactions

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.