What You Should Know About Dietary Supplements

Ashley Clay, MSPAS, PA-C
Medcor Provider

Dietary supplements such as herbs, vitamins, and minerals have become increasingly popular. Americans spend more than $28 billion annually on dietary supplements.

Scientific evidence has suggested that some dietary supplements are beneficial and can help manage certain health conditions, including calcium and vitamin D (for maintaining bone health,) folic acid (for decreasing the likelihood of certain birth defects), and omega-3 fatty acids in fish oil (for lowering the risk of heart disease). However, many supplements require additional research and study before they can be proven effective and safe. It is important to note that the U.S. Food and Drug Administration (FDA) does not evaluate the effectiveness or safety of supplements prior to companies marketing them to the public.

With widespread use of these readily-available products, healthcare providers are increasingly concerned about over-the-counter (OTC) medications and supplements, and their potential for harmful interactions with prescription medications. Supplements can increase or decrease the activity of medications and interact with the potency/concentration of prescription medications and other OTC products.

An additional concern is the way some of these products can affect a patient’s response during surgery or procedures by increasing the risk of bleeding, interfering the anesthesia, altering heart rate or blood pressure, and causing other problems.

Before using any OTC drug, including any supplements, take charge of your health and discuss all your complementary health approaches as well as your diet with your pharmacist or healthcare provider. The more medications a person is taking, the higher likelihood an interaction will occur:

  • If taking 2 medications, there is a 15% chance of an interaction
  • If taking 5 medications, there is a 40% chance of an interaction
  • If taking 7 medications, there is an 80% chance of an interaction

Tips to Avoid Drug Interactions:

  • Ask questions. Talk with your prescribing healthcare provider or pharmacist and inquire about the drugs/supplements you are interested in, if certain food or drinks that may need to be avoided, signs/symptoms of potential interactions, and how the drugs may interact with your body. Visit www.bemedwise.org/questions-about-medicine/ for a sample list of questions to take with you.
  • Report all prescription medications, OTC medications, and supplements (herbs, vitamins, minerals) that you are taking. Report them when you visit your regular healthcare provider, when you have surgery or a procedure, and when you visit the dentist office or chiropractor—anywhere you are seeking medical treatment. Bring a medication list with you to each appointment, ensuring that you include any OTC medication and supplement, and update it as necessary. Consider keeping a medication list on your smartphone.
  • Read the label. Pay attention to directions for use and warnings. Follow instructions for consumption.
  • Fill all your prescriptions from the same pharmacy. This can help flag potential drug-drug interactions.
  • Do some research yourself. Use a drug interaction tool, such as the one on drugs.com or on the AARP website. When researching a particular supplement, avoid commercial sites from sellers. Websites with reliable information include: National Institutes of Health, the Food and Drug Administration, the U.S. Department of Agriculture, and the U.S. National Library of Medicine.
  • Remember, “natural” does not always mean “safe.”

The table below provides some common OTC medications, supplements, foods, and beverages and their potential interactions or areas of concern. Please be advised this is not an all-inclusive list nor are the interactions/concerns described exhaustive.


Cannabidiol (CBD)


Potential for interactions with drugs similar to that of grapefruit juice (below), by raising drug levels in blood. Concerns regarding effect on blood thinners and bleeding risk exist; discuss use prior to surgery or procedure.

Coenzyme Q10 (CoQ10)

May decrease effects of blood thinners thereby increasing risk for clotting; may interact with insulin (used to treat diabetes); may not be compatible with certain cancer treatments.

Ginkgo Biloba

Can increase risk of bleeding—discuss use prior to surgery or procedure; discuss prior to use if diabetic, taking medications for seizures, on blood thinners, or taking NSAIDs (i.e. ibuprofen, naproxen, aspirin); potential to interact with OVER 250 drugs; research has not found a beneficial link between Ginkgo and memory.


Potential to increase heart rate and risk of bleeding; may interact with some blood pressure medications and diabetic medicines; discuss use prior to surgery or procedure.

Grapefruit Juice

Grapefruit juice can alter the amount of medication in your blood, causing enhanced side effects or less effectiveness of certain medications; examples for potential interactions are with medications that treat cholesterol (Lipitor, Zocor), erectile dysfunction medications (Cialis, Viagra), pain medications, antihistamines (Allegra), and psychiatric drugs (buspirone, Tegretol, Valium, Versed, Zoloft).


Avoid if taking other medications such as benzodiazepines (anxiety medication), antihistamines, opioid analgesics, and muscle relaxers—it increases drowsiness; may increase blood glucose levels; discuss with healthcare provider if taking blood thinners or diagnosed with epilepsy; may affect bleeding (discuss use prior to surgery or procedure).


Drugs used to treat high blood pressure, heart disease, kidney disease may change the level of potassium lost in urine, thereby making potassium levels too high in the body. Examples of medications that interfere with potassium output: ACE inhibitors (Lotensin), ARBs (Cozaar), and certain diuretics or “water pills.”

St.  John’s Wort

May prolong the effects of anesthesia; reduce the concentration of other medications; may interact with many drugs including: birth control pills, anti-depressants, anxiety medication, blood thinners (e.g., warfarin), migraine medication (“triptans”), narcotics, cholesterol medicine (statins), diabetes drugs, medications used for heart problems (e.g., digoxin, nifedipine, verapamil, beta-blockers), acid reducers (omeprazole), asthma medication (theophylline), immunosuppressant drugs (cyclosporine), anti-viral agents used in HIV treatment (indinavir), cough medication (Robitussin DM).


When taking antidepressants known as Monoamine Oxidase Inhibitors (MAOIs), tyrosine can result in significant elevations in blood pressure; may also increase levels of thyroid hormones; discuss with your provider if taking Levodopa (used to treat Parkinson’s disease).

Vitamin K

Reduce effectiveness of the blood thinner warfarin; a sudden change in the amount of vitamin K can cause bleeding (less vitamin K) or clotting (more vitamin K).

This article is not intended to diagnose or treat any condition or to give medical advice. Always consult your primary care provider for healthcare instructions. External links are provided as references and do not indicate an endorsement by Medcor. External links are subject to other sites’ terms of use and privacy policies.


American Society of Anesthesiologists, “Herbal and Dietary Supplements and Anesthesia,” https://www.asahq.org/whensecondscount/wp-content/uploads/2017/10/asa_supplements-anesthesia_final.pdf

BeMedWise, https://www.bemedwise.org/

Drugs.com, “18 Herbal Supplements with Risky Drug Interactions,” updated July 8, 2019, https://www.drugs.com/slideshow/herb-drug-interactions-1069

Drugs.com, “Drug Interactions with Grapefruit Juice,” updated August 30, 2019,  https://www.drugs.com/article/grapefruit-drug-interactions.html

Elaine Silvestrini, “Drug Interactions,” DrugWatch, https://www.drugwatch.com/health/drug-interactions/

Mount Sinai, “Tyrosine,” https://www.mountsinai.org/health-library/supplement/tyrosine

National Center for Complementary and Integrative Health, “Coenzyme Q10,” https://nccih.nih.gov/health/coq10

 National Center for Complementary and Integrative Health, “Herb-Drug Interactions,” https://nccih.nih.gov/health/providers/digest/herb-drug

National Center for Complementary and Integrative Health, “Melatonin: What You Need To Know,” https://nccih.nih.gov/health/melatonin#hed6

National Center for Complementary and Integrative Health, “More About St. John’s Wort,” https://nccih.nih.gov/health/know-science/how-medications-supplements-interact?page=5

National Institute of Environmental Health Sciences, “Ginkgo,” https://www.niehs.nih.gov/health/topics/agents/ginkgo/index.cfm

National Institutes of Health, “Dietary Supplements: What You Need to Know,” https://ods.od.nih.gov/HealthInformation/DS_WhatYouNeedToKnow.aspx

National Institutes of Health, “Potassium,” https://ods.od.nih.gov/factsheets/Potassium-Consumer/#h9

National Institutes of Health, “Vitamin K,” https://ods.od.nih.gov/factsheets/VitaminK-Consumer/#h9

Peter Grinspoon, “Cannabidiol (CBD) — what we know and what we don’t,” updated August 27, 2019, https://www.health.harvard.edu/blog/cannabidiol-cbd-what-we-know-and-what-we-dont-2018082414476

Stanford University School of Medicine, “Medications and Herbs That Affect Bleeding,” https://med.stanford.edu/content/dam/sm/ohns/documents/Sinus%20Center/Stanford_Medication_and_Herbs.pdf

U.S. Food and Drug Administration, “5 Things to Consider Before Taking a Dietary Supplement,” https://www.fda.gov/media/106435/download

U.S. Food and Drug Administration, “Tips for Dietary Supplement Users,” https://www.fda.gov/food/information-consumers-using-dietary-supplements/tips-dietary-supplement-users