Nearly 7 in 10 people on prescription medications don’t mention their supplements to their primary care doctor.
That number — roughly 70%, from Pharmacy Times’ survey of U.S. adults — sits at the centre of a problem that gets worse every year. And it’s not because people are hiding things. It’s because the conversation simply doesn’t happen. The doctor doesn’t ask. The patient doesn’t think to bring it up. The supplement bottle sits in the cabinet, invisible to the one person who needs to know it’s there.
Polypharmacy keeps climbing regardless. The share of older adults taking five or more prescription drugs rose from about 31% to 36% over a six-year period, according to a study published in JAMA Internal Medicine. Supplement use rose alongside it — from 52% to 64% in the same window. You don’t need a pharmacology degree to see where this is headed. More medications, more supplements, and nobody talking about how they interact.
So the headline question isn’t “are supplements dangerous?” That’s the wrong framing, and it’s not true as a blanket statement. The question is: in a system where disclosure rates are this low, what’s being missed?
The pairs that worry pharmacists most #
Not all supplement-drug combinations are equally risky. Some cause a clinically silent change in drug levels — your medication gets a little weaker or a little stronger and you’d never notice until something goes wrong. Others are genuinely dangerous, and the evidence on them is not theoretical.
St. John’s wort + antidepressants. St. John’s wort induces CYP3A4, a liver enzyme that breaks down roughly half of all prescription medications (NCCIH). Speed up that enzyme and drugs clear faster — meaning they don’t work as well. The FDA specifically warns against combining St. John’s wort with SSRIs, SNRIs, and other antidepressants because it can trigger serotonin syndrome, a potentially life-threatening condition. It also reduces the effectiveness of birth control pills, immunosuppressants like cyclosporine (risking organ rejection), and some HIV and cancer drugs. If you’re on any long-term prescription, St. John’s wort is not a casual add-on.
Ginkgo, garlic, and ginseng + warfarin or aspirin. All three herbs have antiplatelet properties — they thin the blood — and when you stack them on top of warfarin or aspirin, you’re compounding the bleeding risk. A systematic review across 15 studies (Agbabiaka et al., 2017) found this was the single most reported herb-drug interaction in older adults. The FDA warns about ginkgo-warfarin specifically. A large VA database study (Stoddard et al., 2016) found a hazard ratio of 1.38 for bleeding with ginkgo plus warfarin versus warfarin alone. That’s not a rounding error.
Vitamin K supplements + warfarin. Warfarin works by blocking vitamin K. Sudden increases in vitamin K intake — from a new supplement, or even from a dramatic change in leafy greens — can reverse the anticoagulant effect, leaving you at higher risk of clots (NIH Office of Dietary Supplements). The dose stability that warfarin depends on can be undone by a supplement that looks innocent on the label.
Calcium, iron, and magnesium + antibiotics or thyroid medication. This one is mechanical rather than metabolic. These minerals bind to certain drugs in the gut — tetracyclines, fluoroquinolones, and levothyroxine are the big ones — and prevent absorption. The fix is usually straightforward: space doses by at least two hours. But you have to know to do it, which means someone has to tell you (Changaramkumarath et al., 2025).
Nitrate-boosting supplements + PDE5 inhibitors. Beetroot powder, L-arginine, and other nitric-oxide-boosting supplements can dangerously amplify the blood-pressure-lowering effects of sildenafil (Viagra) and tadalafil (Cialis). This interaction is a known absolute contraindication in prescription labeling, but supplement labels rarely mention it.
And none of this is about one-off interactions in a handful of patients. A comprehensive review published in Cureus (Changaramkumarath et al., 2025) synthesised 16 international studies and found that 12–16% of older adults face a potential supplement-drug interaction. Harvard Health, reporting on the JAMA Internal Medicine data, puts the figure for older adults on a potentially interacting combination at roughly 1 in 6. The exact number depends on which population you’re studying and what you count as an interaction, but the range is consistent enough to take seriously.
Why nobody’s asking — and nobody’s telling #
The disclosure gap isn’t a patient-fault problem. It’s a system-design problem dressed up as a communication failure.
A mixed-methods study by Tarn and colleagues (2019) sat down with 78 patients across primary care, integrative medicine, and naturopathic settings and found something remarkable: patients disclosed only about a third of the supplements they were taking. To primary care physicians specifically, the disclosure rate was just 13% — roughly 1 in 8 supplements ever got mentioned.
And the reasons? The top one, by a margin, was that the provider never asked. After that: patients assumed supplements were “natural, therefore safe,” or didn’t think the visit purpose was related. Not malice. Not secrecy. Just a gap in the routine.
On the provider side, the structural reasons are well-documented. A typical 15-minute appointment doesn’t have a dedicated field in the electronic health record for supplements. Most medical training includes minimal pharmacology education on herbals. And the awkward truth is that many doctors don’t feel confident discussing supplements because the evidence base is uneven and the product quality varies enormously by brand. So both sides of the conversation have a reason to stay quiet.
The brown-bag review: one practical move that costs nothing #
If there’s one action to take from all of this, it’s the brown-bag review. The concept is simple enough that it’s almost embarrassing: gather every supplement, vitamin, herbal product, and over-the-counter remedy you take, put them in a bag — yes, a literal bag — and bring them to your next pharmacist appointment.
Harvard Health and the Cleveland Clinic both recommend this. When you fill all your prescriptions at a single pharmacy, the pharmacist’s system can flag potential interactions — including with supplements you’ve disclosed. The catch, of course, is that last word. The system works if you tell them what you’re taking.
A pharmacist can check your full list against a medication interaction database in minutes. They can tell you which supplements to space apart from which drugs, which combinations need more frequent monitoring (warfarin users, this is especially for you), and which ones should probably be stopped before a procedure. This is literally their job. But they can’t do it for products they don’t know about.
For people who feel awkward raising this with a doctor, the pharmacist route can be lower-stakes — no diagnostic context, just a medication-and-supplement review. There’s a script for it, and it’s short: “I take these supplements along with my prescriptions. Can you check whether any of them conflict?”
Before surgery: two to three weeks matters #
Once you’ve got your complete supplement list together, there’s another context where that list matters even more.
The FDA and NCCIH both say the same thing about surgery: stop certain supplements two to three weeks before any scheduled procedure. The list includes fish oil, ginkgo, garlic, vitamin E, and saw palmetto — anything with antiplatelet or blood-thinning properties. Some supplements can also affect how anesthesia works.
This isn’t a fringe recommendation. It’s federal guidance. And because a significant share of supplement users are older adults — the same population most likely to be on blood thinners or to face surgery — the overlap between “doesn’t know about this recommendation” and “needs it” is uncomfortably large.
If you’re scheduled for surgery, tell both the surgeon and the anesthesiologist about every supplement you take. This includes the things you don’t think of as supplements: protein powders, sleep aids, herbal teas you drink daily, the magnesium you take at night.
If you’re pregnant, breastfeeding, or considering supplements for a child, the stakes are higher — most herbal supplements haven’t been tested for safety in these groups, and the NCCIH and NIH both advise caution beyond standard prenatal vitamins.
The regulatory piece you should understand #
Dietary supplements in the U.S. don’t go through FDA pre-market approval for safety or effectiveness. The FDA can act after problems are reported — it received over 2,000 adverse event reports related to dietary supplements in 2023 (per the Dietary Supplement Listing Act of 2026) — but the gatekeeping function that exists for prescription drugs simply isn’t there for supplements (FDA, NCCIH, NIH ODS).
That’s not an argument against supplements. It’s context for why the burden of interaction checking falls on you, your pharmacist, and your doctor rather than on the regulatory system. The framework simply isn’t designed to catch these things at the approval stage because there is no approval stage.
What this isn’t #
If you take supplements and you’re on medication, the answer is not to stop taking supplements. For a lot of people, supplements genuinely help — with sleep, with specific deficiencies, with symptom management. The evidence base for some is solid; for others, it’s thin but the individual experience is real.
The answer is disclosure. A complete list. One pharmacy. A conversation with the pharmacist. A note in the medical record. The problem isn’t the supplements. The problem is nobody talking about them.
None of the fixes here require anyone to become an expert in herb-drug pharmacology. They require exactly one person — you — to put everything on the table and ask one question. After that, the professionals can do what they’re trained to do.