As the use of medications and dietary supplements rises in the U.S., does that mean that more consumers could be at risk of negative interactions between drugs and supplements? This was the question researchers asked in a study published last year in JAMA Internal Medicine.(1)
Based on survey data, the researchers found that the use of both prescription medications and dietary supplements in older U.S. adults increased in 2005–2011. Those researchers noted a growing risk of a few drug and dietary supplement interactions in particular, including warfarin sodium and omega-3 fish oil, or warfarin sodium and garlic. For the most part, however, most of the interactions observed in the study were between different types of drugs, and not between drugs and supplements.
That seems to be the consensus—that negative interactions between drugs and supplements are rare, but that continued research is still vital to ensure patient safety.
“There’s a lot of literature suggesting that almost every herb interacts with almost every drug and is potentially dangerous,” says Stefan Gafner, PhD, chief science officer for the American Botanical Council (Austin, TX). “But that’s based on studies of isolated enzymes and cell cultures. The (clinical) occurrence of herb-drug interactions is quite low. It’s mostly a concern for healthcare professionals and government, but I’ve also seen industry members come up with new tools to predict interactions.”
Consumers should always contact their healthcare provider if they have concerns about how their nutritional supplements may interact with their prescription drugs. In the meantime, here are just a few of the lesser-known potential interactions between drugs and supplements that might not always be at top of mind, but that manufacturers and consumers should know about.
1. Qato DM et al. “Changes in prescription and over-the-counter medication and dietary supplement use among older adults in the United States, 2005 vs 2011.” JAMA Internal Medicine, vol. 176, no. 4 (2016): 473-482
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Mineral Supplements and Thyroid Medication
Douglas “Duffy” MacKay, ND, is a naturopathic doctor and the senior vice president of scientific and regulatory affairs for the Council for Responsible Nutrition (Washington, DC). MacKay notes that mineral supplements in particular can interact with several medications.
“When you take a supplement like calcium or magnesium—a larger mineral—it can compete for absorption with other things,” MacKay says. “Any drug that you have to take on an empty stomach, like thyroid medication, can interact with minerals. Calcium and magnesium behave like food and block the absorption of those drugs.”
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Schisandra Extract and Cyclosporine
Schisandra extract (Schisandra chinensis) is an herb used for stress relief, energy support, and sexual health.(2) Gafner says that, depending on the duration of use, schisandra extract may interact with drugs that are metabolized by the enzyme cytochrome P450 3A4. These include drugs like antifungal medications and chemotherapy drugs.
“There are lots of potential interactions [with schisandra extract]—the list is a long one,” says Gafner. “It can also interact with opioids, antidepressants, and benzodiazepines.”
In vivo animal laboratory studies have found that schisandra extract can increase the bioavailability of the drug cyclosporine in rats.(3) Safety notes published by supplement manufacturer MediHerb indicate that schisandra extract may amplify the effects of the sleep aid midazolam.(4)
2. Panossian A et al. “Pharmacology of Schisandra chinensis Bail.: an overview of Russian research and uses in medicine.” Journal of Ethnopharmacology, vol. 118, no. 2 (2008): 183-212
3. Xue XP et al. “Effect of Wuzhi tablet (Schisandra sphenanthera extract) on the pharmacokinetics of cyclosporin A in rats.” Phytotherapy Research, vol. 17, no. 8 (2013): 1255-1259
4. MediHerb. ”Potential herb-drug interactions for commonly used herbs.” https://www.standardprocess.com/MediHerb-Document-Library/Catalog-Files/herb-drug-interaction-chart.pdf
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Warfarin and Ginseng/Kale
One of the most important drugs to monitor for potential interactions is warfarin. “This single medication interacts with hundreds of different supplements, as well as food,” MacKay says. A 2004 clinical study at the University of Chicago found that ginseng (Panax ginseng) can reduce warfarin’s blood-thinning effects, for instance.(5)
Kale supplements can also be problematic. The National Institutes of Health says that foods rich in vitamin K, including kale, can decrease warfarin’s effectiveness.(6)
5. Yuan C et al. “Brief communication: American ginseng reduces warfarin’s effect in healthy patients.” Annals of Internal Medicine, vol. 141, no. 1 (2004): 23-27
6. National Institutes of Health Clinical Center. “Important information to know when you are taking: Warfarin (Coumadin) and vitamin K.” Important Drug and Food Information. https://www.cc.nih.gov/ccc/patient_education/drug_nutrient/coumadin1.pdf
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Vitamin B12 and Antacids
While antacids might not lead to interactions that are life-threatening, they can reduce the bioavailability of certain supplements. MacKay notes that by blocking the production of stomach acid, antacids prevent the body from absorbing an array of nutrients, including vitamin B12 and folic acid.
“So here’s one single drug that’s very popular, widely prescribed, with a clinically meaningful impact on nutrient levels,” MacKay says. “And it gets more dramatic as we age. [It’s particularly a problem for] people who have been institutionalized and are taking a lot of medications.”
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Drug-Supplement Interactions Are a Manageable Risk
Interactions between drugs and supplements are a manageable risk that can be reduced through proper quality control and patient education. Professional conferences, physician outreach, and thorough patient-advisory notes can improve patient safety and prevent the rise of harmful interactions.
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