11 common drug-nutrient interactions according to a pharmacist - Blog - Persona Nutrition

11 common drug-nutrient interactions according to a pharmacist

When someone takes a prescription medication – whether it’s something they’re on indefinitely or something they’re taking short term – that prescription medication may change the way the body absorbs or utilizes certain micronutrients, raising overall levels, especially if the person is also supplementing with a daily vitamin. And, on the flip side, the daily vitamin, herb or other supplement may impact the effectiveness of the medication.

These are called drug-nutrient interactions (DNIs) and they play in important part in overall wellness. DNIs can have a lasting impact on a person’s health and wellness, but they are rarely discussed.

As a community pharmacist, I’m on the front lines of dispensing prescriptions and seeing someone checkout with a daily multivitamin in their hand; I always ask, “did you check with your doctor to make sure there aren’t any interactions.” And, 100% of the time, I get the response “no, I didn’t realize I should.”

Many times, individuals will stop taking their prescription medication because they experience increased fatigue or other issues. They don’t realize their prescription medication can interact with their over-the-counter vitamins or supplements. That’s why it’s critical for people to check with their health care practitioner or use a personalized vitamin program that cross-references DNIs (like Persona) before adding a supplement to their routine.

As a pharmacist and medical advisory board member for Persona Nutrition, I’m sharing the most common drug-nutrient interactions I see on a regular basis to help keep consumers safe.  

Immunity and DNIs

During cold and flu season, people stock up on immunity-supporting nutrients like vitamin C, vitamin D and zinc. Because dietary supplements – including those for immunity – are readily accessible over the counter, many people don’t even think about speaking with their health care provider before adding them to their daily routine.  

The following are three of the most prominent drug interaction concerns among ingredients found in immunity-supporting supplements or therapies:

  1. Zinc—When taken simultaneously with some medications, zinc can bind with the drug in the stomach and form complexes making it more difficult for the body to absorb the medication. This is a common interaction with thyroid medications and certain types of antibiotics. 1 With zinc containing supplements, it is often important to separate administration from medications by 2 to 4 hours to avoid this type of interaction.
  2. Vitamin C—Vitamin C may increase estrogen levels by altering the way they body metabolizes the hormone.2 This effect is usually more pronounced with the higher doses of vitamin C commonly found in immunity supplements. This can increase the side effects a patient may experience in particular with hormone replacement therapy or oral contraceptives containing estrogen.
  3. Immunosuppressive therapy—Immunity supplements may not be appropriate to take with drug therapies that are designed to suppress components of a person’s immune system. Patient’s using immunosuppressive therapies, such as those designed to treat specific types of cancer or autoimmune disorders, should consult their health care provider prior to taking any supplement that may stimulate their immune system.

Other common interactions

In addition to the immunity-focused interactions, there are eight other interactions that have been flagged as the most popular from Persona’s database of more than 2,500 prescription medications.

High blood pressure medications

  • Antihypertensives + Garlic – Garlic has been shown to lower blood pressure and may have interfere with the metabolism and clearance of certain types of antihypertensives. For those taking antihypertensives, garlic supplements may have an additive effect with these prescription drugs and should be avoided. 3,4
  • Diuretics + Fish Oil – Diuretics help rid the body of salt and extra fluid by increasing urination. Diuretics are commonly used in those with high blood pressure or heart failure. Because diuretics can decrease blood pressure, when combined with supplements that may also lower blood pressure, diuretics could potentially increase risk for hypotension. 5

Medications for mood

  • Antidepressants + 5-HTP – 5-HTP is a precursor of serotonin. Combining supplemental 5-HTP with antidepressant medications that increase serotonin levels in the brain could theoretically lead to serotonin syndrome, a dangerous overload of serotonin in the brain. Common side effects of serotonin syndrome include headache, confusion, and loss of muscle coordination, but in severe cases result in irregular heart rhythm or seizure. 6,7
  • Anxiety medications + Grapefruit – Grapefruit can interfere with certain antianxiety medications by altering enzymes responsible for transporting these medications into the blood stream and the breakdown of these medications. This results in increased side effects of antianxiety medications, like prolonged sedation. 8 Grapefruit should be avoided with antianxiety medications to ensure appropriate levels of medications in the blood stream.

Blood thinning medications

  • Warfarin + Vitamin K – Certain anticoagulants work to thin the blood by preventing the body from making clotting factors. Vitamin K is an essential vitamin to promote normal amounts of blood clotting in the body and preventing excessive bleeding. However, when combined, vitamin K can work against these anticoagulant medications and increase the risk for a blood clot. 9

Birth control

  • Oral Contraceptives + Green Tea Extract – Certain oral contraceptives can decrease caffeine clearance in the body by up to 65%, which can increase the effects of caffeine in green tea. 10, 11 To avoid an additive effect, Green Tea Extract supplementation should be avoided in those taking oral contraceptives.
  • Oral Contraceptives + Garlic – Garlic can enhance the metabolism of certain hormones by amplifying the enzymes responsible for clearing this class of drugs. Garlic should be avoided with oral contraceptives to ensure the drug is not cleared too quickly from the body, potentially make the medication less effective.12

Medications that change responses of the immune system

  • Immunosuppressant therapy + Spirulina – Spirulina is thought to stimulate the body’s immune system.13, 14 Immunosuppressant therapies, commonly used to treat Crohn’s disease and psoriasis, can be less effective if the body’s immune system is activated. ­­­Spirulina should be avoided when taking immunosuppressant drugs to ensure effective therapy.

Cholesterol medications

  • Statins + CoQ10 – Cholesterol lowering medications, called statins, block your body from producing cholesterol. Through this process, they also block your body from producing CoEnzyme Q10, a naturally occurring enzyme that plays a role in muscle energy production.15 It is thought that using a CoEnzyme Q10 supplement may reduce side effects of muscle pain and discomfort in patients taking a statin therapy.

Diabetes medications

  • Antidiabetic Medications + Ashwagandha – Preliminary evidence shows that ashwagandha root powder can decrease blood glucose. 16, 17 To avoid an additive effect of blood sugar becoming too low, Ashwagandha should be avoided with those taking blood sugar lowering drugs.

Thyroid medications

  • Thyroid medications + Iron – When taken simultaneously, thyroid medications and iron form insoluble complexes in the gastrointestinal tract preventing the absorption of thyroid medication into the blood stream. 18 Iron supplements should be taken at least two hours apart from thyroid medications to ensure complete absorption of the drug.

Speak with your doctor, pharmacist, or nutritionist to better understand any possible DNIs prior to starting a new medication or nutritional supplement program.


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  2. Vihtamaki T, Parantainen J, Koivisto AM, et al. Oral ascorbic acid increases plasma oestradiol during postmenopausal hormone replacement therapy. Maturitas 2002;42:129-35.
  3. Ried K, Frank OR, Stocks NP. Aged garlic extract reduces blood pressure in hypertensives: a dose-response trial. Eur J Clin Nutr 2013;67(1):64-70.
  4. Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: An updated meta-analysis and review. J Nutr. 2016;146(2):389S-396S.
  5. Appel, L. J., Miller, E. R., III, Seidler, A. J., and Whelton, P. K. Does supplementation of diet with ‘fish oil’ reduce blood pressure? A meta-analysis of controlled clinical trials. Arch Intern Med 6-28-1993;153(12):1429-1438.
  6. Lowe SL, Yeo KP, Teng L, et. Al. L-5-Hydroxytryptophan augments the neuroendocrine response to SSRI. Psychoneuroendocrinology. 2006; 31(4): 473-484
  7. Pardo JV. Mania following addition of hydroxytryptophan to monoamine oxidase inhibitor. Gen Hosp Psychiatry 2012;34(1): 102. e13-4.
  8. Sugimoto, K., Araki, N., Ohmori, M., Harada, K., Cui, Y., Tsuruoka, S., Kawaguchi, A., and Fujimura, A. Interaction between grapefruit juice and hypnotic drugs: comparison of triazolam and quazepam. Eur J Clin Pharmacol 2006;62(3):209-215.
  9. Booth SL. Dietary vitamin K guidance: an effective strategy for stable control of oral anticoagulation? Nutr Rev. 2010;68(3):178-81.
  10. Haller CA, Jacob P 3rd, Benowitz NL. Pharmacology of ephedra alkaloids and caffeine after single-dose dietary supplement use. Clin Pharmacol Ther 2002;71:421-32.
  11. Pollock BG, Wylie M, Stack JA, et al. Inhibition of caffeine metabolism by estrogen replacement therapy in postmenopausal women. J Clin Pharmacol 199; 39; 936-40.
  12. Zhang N, Shon J, Kim MJ, et al. Role of CYP3A in Oral Contraceptives Clearance. Clin Transl Sci. 2018;11(3):251–260.
  13. Mao TK, Van de Water J, Gershwin ME. Effects of a Spirulina-based dietary supplement on cytokine production from allergic rhinitis patients. J Med Food 2005;8:27-30.
  14. Karkos PD, Leong SC, Karkos CD, et al. Spirulina in clinical practice: evidence-based human applications. Evid Based Complement Alternat Med 2011;531053. doi: 10.1093/ecam/nen058. Epub 2010 Oct 19.
  15. Berthold HK, Naini A, Di Mauro S, et al. Effect of ezetimibe and/or simvastatin on coenzyme Q10 levels in plasma: a randomised trial. Drug Saf 2006;29:703-12.
  16. Andallu B, Radhika B. Hypoglycemic, diuretic and hypocholesterolemic effect of winter cherry (Withania somnifera, Dunal) root. Indian J Exp Biol 2000;38:607-9.
  17. Agnihotri AP, Sontakke SD, Thawani VR, Saoji A, Goswami VS. Effects of Withania somnifera in patients of schizophrenia: a randomized, double blind, placebo controlled pilot trial study. Indian J Pharmacol. 2013;45(4):417-8.
  18. Campbell NRC, Hasinoff BB, Stalts H, et al. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Int Med 1992;117:1010-3.

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