Herbal Supplements and Prescription Drugs: Interactions to Watch Out For

Written By: Christina Newberry

Reviewed By: Gloria Tsang, RD

Title: Registered Dietitian

Last Updated on:

You probably know that before filling a prescription, you should make sure your doctor and pharmacist know about all the other medications you’re taking to avoid potential interactions that can change how your medications work. But did you know that it’s equally important to consider the potential interactions between your medications and herbal supplements?

Tell Your Doctor About All Drugs and Supplements You Use

Herbal supplements are hugely popular and readily available. If you toss bottles of herbal supplements in your basket while shopping at a health food store, you might think of them as being more like food products than medications. But the truth is that herbal supplements have potent effects that can interfere with both prescription and non-prescription medications.

According to IDA Cambie pharmacy manager Edwin Kwong, R.Ph, that potential interaction should not be taken lightly. “As well as a graying population that may be on multiple medication treatment for various common ailments such as hypertension, heart disease, and diabetes, we can expect that herbal–drug interactions could be a real concern from a safety and therapeutic point of view,” Kwong said.


Herbal supplements may decrease a drug’s effectiveness or, conversely, amplify the effects to a dangerous level. Kwong warns patients to be especially careful about taking herbal and drug products that serve the same purpose. Herbal supplements can also increase your risk of experiencing drug side effects. That’s why it’s always important to tell your doctor and your pharmacist about any herbal supplements you’re taking, especially before filling a new prescription.

Likewise, it’s important to ask a health professional about potential interactions with your existing medications before buying a new herbal supplement. If your doctor is not interested in herbal supplementation or is not willing to address your questions about supplements, your pharmacist can be an important resource.

“As a frontline and easily accessible healthcare professional, pharmacists are in an ideal position to intervene and educate the public on the potential benefit and risk of these alternative and complementary medications,” Kwong said.

Common Herb–Drug Interactions

Supplement Use May interact with…
Bilberry May help improve eye health Anti-coagulants; anti-platelet medicationsNote: Diabetics should use with caution because it may lower blood sugar
Black Cohosh Menopause symptom relief Acetaminophen (Tylenol); antibiotics and antidepressants; cisplatin (a cancer drug); heart medications;
Cranberry Urinary tract infections Anti-coagulants; anti-platelet medicationsNote: Diabetics should be careful if using cranberry juice because many cranberry juices on the  market contain high amounts of sugar.
Dong Quai Menopause symptom relief Antibiotics; anti-coagulants; St John’s wort
Echinacea Immunity booster Allergy and asthma medications; anti-anxiety medications; antibiotics; antifungal medications; diabetes medications; heart medications; HIV medications
Feverfew Migraine relief Anti-coagulants; migraine medications
Garlic May help lower cholesterol and prevent blood clots Anti-coagulants; anti-hypertensives; anti-platelet medications; diabetes medications; HIV medications; oral contraceptives (“the pill”)
Gingko Biloba May help improve circulation and memory Anti-coagulants; anti-platelet medications; monoamine oxidase inhibitors (MAOIs)Note: Lowers seizure threshold.
Ginseng May help reduce stress, boost energy, improve stamina, and lower cholesterol Antidepressants; heart and high blood pressure medicationsNote: Ginseng can increase blood pressure. Overuse can lead to headaches, insomnia, and heart palpitations. Diabetics should use with caution because it may increase blood sugar.
Green Tea Weight loss Acetaminophen (Tylenol); diabetes medications; heart medications
Hawthorn May help lower blood pressure and cholesterol Digoxin
Kava May help address insomnia and anxiety Alcohol; antidepressants; sedativesNote: Do not take ​kava if you have a history of liver problems.
Licorice May help to treat coughs, colds, and peptic ulcers Diuretics; digoxinNote: High doses of licorice can lead to increased blood pressure, water retention, and potassium loss.
Milk Thistle May help with liver, kidney, and gall bladder issues Allergy medications; antifungals; estrogen and oral contraceptives (“the pill”); heart medications; sedatives
Saw Palmetto May help with urinary and prostate issues Blood thinners; estrogen and oral contraceptives (“the pill”); Propecia
St. John’s Wort May help to treat mild to moderate depression Allergy and asthma medications; antidepressants; erectile dysfunction drugs; heart/blood-thinning medications; HIV medications; narcotic medications; oral contraceptives (“the pill”);  Tamoxifen (a cancer drug)
Valerian A mild sedative Alcohol, sedatives

Keep in mind this list does not include all the potential drug–herb interactions, as there’s no way we could list them all in one article. Do not assume that supplements or drugs not listed here are safe to combine.

The Bottom Line

Herbal supplements can have powerful effects – both positive and negative – and mixing them with drugs can be risky. Remember: Talk to your doctor or pharmacists for the best, most current and personalized advice.

Sources: Consumer Reports, IDA Cambie Pharmacy, Mayo Clinic


drugs, herbs, medication, supplements


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