Surveys suggest that about 75% of Americans use dietary supplements. Many also take prescription medications – opening the door for various drug-supplement interactions. Let’s review a few.
Keep glucosamine on your radar. Taking glucosamine with warfarin might increase INR and increase the risk of bruising and bleeding. This interaction has been reported in patients taking glucosamine with and without chondroitin. It’s a concern for older patients as both agents are commonly used in this population. Warn about this potential interaction and advise patients to avoid taking glucosamine if they’ve been prescribed warfarin.
Also ask patients about magnesium. Magnesium has seen a major surge in popularity over the past several years – it’s held a steady spot on Amazon’s list of the top 10 selling supplements for a while now. While it’s likely safe when used appropriately, counsel patients that it has the potential to interfere with the absorption of various drugs, particularly quinolone and tetracycline antibiotics. Taking magnesium with these antibiotics can decrease their absorption and effectiveness. To avoid this interaction, advise separating administration of magnesium and these antibiotics. For example, take a quinolone antibiotic at least 2 hours before, or 4 to 6 hours after, magnesium supplements.
Lastly, reiterate concerns about fruit juices. Certain fruit juices, including orange, apple and grapefruit, can alter the absorption of over 50% of prescription medications – due to the inhibition or induction of enzymes (including cytochrome P450, or CYP, enzymes) or transporters (such as organic anion-transporting polypeptides, or OATP). To be safe, advise separating most fruit juices from prescription drugs by at least 4 hours.
Refer to our resource on Drug-Supplement Interactions for a quick reference on other common interactions, including severity ratings so you know which ones to really monitor. And take advantage of our Interactions Checker to screen for possible interactions between multiple agents at once.
The information in this brief report is intended for informational purposes only, and is meant to help users better understand health concerns. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions. Copyright © 2025 NatMed. Commercial distribution or reproduction prohibited. NatMed is the leading provider of high-quality, evidence-based, clinically-relevant information on natural medicine, dietary supplements, herbs, vitamins, minerals, functional foods, diets, complementary practices, CAM modalities, exercises and medical conditions. Monograph sections include interactions with herbs, drugs, foods and labs, contraindications, depletions, dosing, toxicology, adverse effects, pregnancy and lactation data, synonyms, safety and effectiveness.
