Many people take dietary supplements to improve their health. Many people also take one or more medications for various health conditions. There are several known medication-nutrient interactions that people must be aware of – this post will highlight some of the most important interactions person’s taking these substances need to be aware of.

According to the Council on Responsible Nutrition, 77% of Americans reported taking dietary supplements in 2019. In addition, more than 66% of Americans use prescription medications. Knowing this, there is obvious overlap between these two groups. However, most people are unaware of potential interactions between the medications and supplements they are taking.

There are many sources of information that consumer’s can use to try and find the known and possible interactions between medications and nutrients. We’ve highlighted several of these in a previous post: Medication-Herb Interactions. Other good sources include the Therapeutic Research Centers Natural Medicines Database and PubMed.

Note that most of the information on medication-nutrients interactions focus on nutrient depletion, which can be extensive as both over-the-counter (OTC) and prescription medications can negatively influence nutrient digestion, absorption, distribution, metabolism, function, catabolism (breakdown) and excretion. On the flip side, some vitamins, minerals and other nutrients can either increase or decrease the absorption of specific medications, which can contribute to adverse effects. Here are a couple of examples:

  • Iron and zinc can reduce the intestinal absorption of many antibiotics, thereby reducing the medication’s efficacy.
  • Calcium and iron supplements can decrease the absorption of levothyroxine, which may require an increase in dose of the medication.
  • Vitamin B6 can reduce or negate the effects of carbidopa-levodopa combinations, which is a medication that is used for those with Parkinson’s Disease

Here are several other important medication-nutrient interactions (for more complete information, see this white paper):

Medication Nutrient Interaction

Vicodin, Norco

Caffeine Increases analgesic effects

Increases absorption

Increases elimination of drug

Increases risk of liver toxicity


Levothroid, Synthroid



Vitamin C



Decreases absorption of drug; increases TSH

Increases absorption of drug; decreases TSH

Decreases absorption of drug


Glucophage XL, Gluformin

Berberine (300 mg)



Alcohol (>7 drinks/week)

Improves insulin sensitivity; decreases HOMA-IR, total cholesterol, LDL-C

Increase effects of drug; increases lactic acidosis and lactate production



EGCG Significantly reduces systemic exposure of drug

If you are taking medications, be sure and ask your pharmacist  as well as your health care provider about possible interactions. Always remember, there is no substitute for doing your own research as well – your health is worth it.



  1. Mohn, E. S., Kern, H. J., Saltzman, E., Mitmesser, S. H., & McKay, D. L. (2018). Evidence of Drug-Nutrient Interactions with Chronic Use of Commonly Prescribed Medications: An Update. Pharmaceutics, 10(1), 36. PMC5874849/#!po=43.6275
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  4. Duntas, L. H., & Jonklaas, J. (2019). Levothyroxine dose adjustment to optimize therapy throughout a patient’s lifetime. Adv Ther, 36, S30-S46.
  5. Mason, P. (2010). Important drug-nutrient interactions. Proceedings of the Nutrition Society, 69(4), 551-557. society/article/important drug nutrient-interactions/47E373947A2F248374EF59D291BAA5AB/core-reader#
  6. Addressing pharmaceutical interactions in clinical practice.