When Supplements and Meds Don’t Mix
June 2025
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.
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.