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Do your supplements interact with your prescription medications?

Posted on: January 6, 2013   by  John Cannell, MD


The majority of Americans take at least one vitamin or supplement and the market is growing. The global market is worth $84 billion for vitamins and minerals and has grown by 12% per year in the past five years. Vitamin D is among the most rapidly growing supplement.

Hodgson J  Consumer, Drug Firms Vie in Vitamins . Wall Street Journal, Dec 2, 2012

Have you ever wondered if any of your vitamins or supplements interacts with your prescription medications? Recently, Dr. Tsai of the China Medical University teamed up with experts in Illinois to review the entire issue.

Tsai HH, Lin HW, Simon Pickard A, Tsai HY, Mahady GB. Evaluation of documented drug interactions and contraindications associated with herbs and dietary supplements: a systematic literature review. Int J Clin Pract. 2012 Nov;66(11):1056-78.

The authors made the following points:

  • The five most likely supplements to cause drug interactions are St. John’s wart, gingko, kava, digitalis, and willow.
  • The medications that interacted with supplements the most often are warfarin (Coumadin), insulin, aspirin, digoxin and ticlopidine (Ticlid).
  • Saint John’s wart has the most severe interaction warnings. It decreases the effectiveness of many medications, including alprazolam (Xanax), amitriptyline (Elavil), imatinib (Gleevec), midazolam (Versed), nifedipine (Procardia), and verapamil (Calan), and it interacts with a number of atypical antipsychotics like Risperdal and Zyprexa.
  • Warfarin (Coumadin) is known to have more than 100 interactions with supplements.
  • 5-hydroxytrytophan interacts with many antidepressants causing the serotonin syndrome.
  • Some of the contraindications were suspicious, such as flax seed, a food, being contraindicated in diarrhea, hyperlipidemia, and prostate cancer.
  • Herbs were more likely to have interactions with drugs then were vitamins and minerals.

In my opinion, some of the warnings lead doctors to be too conservative in their recognition of mineral deficiencies. For example, magnesium was listed as causing multiple interactions, but, in the absence of magnesium overdose, such as is often ordered by doctors to clean out the colon, magnesium deficiency is the real problem. The following review, which is free to download, is a good source of information about magnesium deficiency, how common it is, and why a blood magnesium levels cannot detect it.

Swaminathan  R. Magnesium metabolism and its disorders. Clin Biochem Rev. 2003 May;24(2):47-66.

The exception is advanced renal failure, where high blood magnesium is common, or drowning in the Dead Sea, where high blood magnesium is routine.

Oren S, Rapoport J, Zlotnik M, Brami JL, Heimer D, Chaimovitz C. Extreme hypermagnesemia due to ingestion of Dead Sea water. Nephron. 1987;47(3):199-201.

Many of you may want to know what/if vitamin D interacts with any drugs. Care is needed in the following situations:

  • If you’re taking certain other medicines: digoxin and have irregular heartbeats (atrial fibrillation) or thiazide diuretics such as hydrochlorothiazide or bendroflumethiazide (commonly used to treat high blood pressure). In this situation, don’t take high doses of vitamin D without consulting your doctor.  You should also have your digoxin level monitored more closely if you’re taking vitamin D.
  • If you have one of these medical conditions: primary hyperparathyroidism, Hodgkin’s or non-Hodgkin’s lymphoma, a granulomatous disease, kidney stones, some types of kidney disease, liver disease or hormonal disease, you should get advice from your doctor or a specialist before taking high doses of vitamin D.
  • Don’t take vitamin D if you have high blood calcium levels, unless under the care of your physician.
  • You may need more than the usual dose of vitamin D if you’re taking certain medicines which interfere with vitamin D. These include: carbamazepine, phenytoin, primidone, barbiturates and some medicines used for the treatment of HIV infection.

For a list of contraindications for other vitamins and minerals, visit the Office of Dietary Supplement’s website:


2 Responses to Do your supplements interact with your prescription medications?

  1. Rita and Misty

    Interesting that the five most likely supplements to cause drug interactions are St. John’s wort, gingko, kava, digitalis, and willow.

    All five supplements listed are (imo) worthwhile supplements in their own right and certainly worth a try prior to moving on to similar prescription meds….

    Re: magnesium–thank goodness not too many of us need to worry about drowning in the Dead Sea (ha)!!!!

    Seriously, though, magnesium deficiency is a huge problem…and another area where GPs knowledge may fall short….

  2. Kata76

    Dear Dr Cannell,

    Thank you for this post! Well… I take the drug Olmetec for high blood pressure (just googled, it has hydrochlorothiazide in it). You write, “don’t take high doses of vitamin D without consulting your doctor”, what do you mean by “high doses”? I take 50’000 IU per week of Vitamin D, is this a high dose? I don’t think my doctor has enough Information about Vit D… what should I do?

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