Vitamins, Probiotics & Herbal Supplements: A Pharmacist's Guide to Natural Health Products
In Canada, vitamins, minerals, probiotics, and herbal remedies are officially called Natural Health Products (NHPs) and are regulated by Health Canada. "Natural" doesn't mean "no effect" — many NHPs are active enough to interact with prescription medication, change how a drug is absorbed, or affect lab results. Here's what our pharmacists want every patient to know before adding one to their routine.
What counts as a Natural Health Product?
Any licensed NHP carries an 8-digit NPN (Natural Product Number) or DIN-HM on the label — Health Canada's confirmation that the product has been reviewed for safety, quality, and the health claims on the package. It's worth checking for this number before buying any vitamin, probiotic, or herbal product, since it's the easiest way to tell a properly regulated product apart from one with no oversight at all.
Vitamins & minerals
Most people don't need a multivitamin if they eat a varied diet, but specific situations change that:
- Vitamin D — recommended for most adults in Canada during fall/winter, and for infants, older adults, and anyone with limited sun exposure year-round.
- Vitamin B12 — often low in patients on metformin or long-term acid-reducing medication, and in anyone following a fully plant-based diet.
- Iron — should generally be confirmed with a blood test before starting; taking iron without a true deficiency can cause GI upset for no benefit.
- Calcium — works best in smaller, divided doses, and can reduce the absorption of some thyroid medications and antibiotics if taken at the same time.
Probiotics
Probiotics are most studied for preventing antibiotic-associated diarrhea and supporting recovery after a GI illness. A few practical points:
- If taken alongside an antibiotic, space the two doses 2–3 hours apart so the antibiotic doesn't kill the probiotic strain before it has a chance to work.
- Strains matter — the evidence for one probiotic product doesn't automatically apply to a different brand or strain.
- Most healthy adults tolerate probiotics well, but anyone who is immunocompromised should check with a pharmacist or doctor first.
Herbal remedies — where most interactions happen
This is the category that most often surprises patients. A few common examples we see at the pharmacy counter:
- St. John's Wort — interacts with a long list of medications, including birth control, antidepressants, and blood thinners. It can make some prescriptions noticeably less effective.
- Fish oil / omega-3 — at high doses can add to the effect of blood thinners like warfarin or apixaban, increasing bleeding risk.
- Melatonin — generally well tolerated, but can increase drowsiness when combined with other sedating medications.
- Turmeric / curcumin in supplement (not cooking) doses can also affect blood thinners and certain diabetes medications.
- Vitamin K supplements and vitamin-K-rich green supplements can directly counteract warfarin.
None of this means these products are unsafe to use — it means timing, dose, and your specific prescriptions all matter, and that's exactly the kind of check a pharmacist is trained to do quickly.
How to choose safely
- Look for the NPN/DIN-HM on the label.
- Tell us about every supplement you take, the same way you would a prescription — bring the bottle in if you're not sure of the name.
- Run it through our Drug Interaction Checker or ask at the counter before starting something new.
- Start one product at a time so it's easy to tell what's helping (or causing a side effect).
If you take three or more medications already, the most thorough way to check your full supplement list at once is a Medication Review (MedsCheck) — bring every bottle, prescription and natural health product alike, and we'll go through all of it together.
Starting a new vitamin, probiotic, or herbal product?
Bring it in or ask at the counter — we'll check it against your current medications in minutes, free, no appointment needed.
Check an Interaction → Book a Medication Review →This article is general information, not medical advice. Always tell your pharmacist or doctor about every natural health product you take alongside prescription medication.