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Healthy ageing · Answer

Which supplements interact with common medicines in South Africa?

Supplements that most often interact with common South African medicines include St John's wort, vitamin K and high-dose fish oil with warfarin, red yeast rice with statins, potassium with blood-pressure tablets, and calcium, iron or magnesium with thyroid or antibiotic medicines. Ask a pharmacist to review every product you take, including herbal ones.

· 2 min read

Which supplements interact with common medicines?

Interactions are more likely in older adults because they take more medicines and have reduced kidney and liver clearance. Supplements are not always harmless extras: some change how drugs are absorbed, processed or how strongly they act. Unregistered complementary medicines sold in South Africa must carry a SAHPRA disclaimer saying they have not been evaluated, so a label does not prove safety.

Which combinations matter most?

MedicineSupplementConcern
WarfarinVitamin K (including D3+K2 products and some multivitamins)changes anticoagulant effect
Warfarin, aspirin, other blood thinnersHigh-dose fish oil, ginkgo, vitamin Eextra bleeding tendency
Warfarin, many othersSt John's wortinduces enzymes and can reduce drug levels
StatinsRed yeast ricecontains a lovastatin-like compound, so doubling up
ACE inhibitors, ARBs, spironolactonePotassium supplements, salt substitutesraised blood potassium
Thiazide diureticsCalcium and vitamin Draised blood calcium
LevothyroxineCalcium, iron, magnesiumpoorer absorption if taken together
Tetracycline or quinolone antibiotics, bisphosphonatesMagnesium, iron, calcium, zincpoorer absorption
Metformin, acid-reducing medicinesSupplements are not the issuelong-term use can lower B12 (and magnesium with acid reducers)

What practical rules help?

  • Space doses: keep calcium, iron and magnesium a few hours away from thyroid, antibiotic and bisphosphonate medicines, as your pharmacist advises.
  • Do not self-start St John's wort if you take any regular medicine.
  • Check "electrolyte" and "salt" products if you have high blood pressure, heart or kidney disease; many contain sodium or potassium.
  • Warfarin patients: tell your clinic about any vitamin K, fish oil, herbal or multivitamin product and keep intake steady.
  • Kidney disease: magnesium supplements and creatine need medical sign-off. See supplements and kidney disease.

What about the supplements people ask about most?

For omega-3, the 2025 ISSN position stand notes that high doses may increase bleeding tendency with anticoagulants. For vitamin D, the issues are calcium with thiazides and, with K2 combinations, warfarin. See vitamin D and B12 over 60, CoQ10 and glucosamine and chondroitin for specific product notes.

How do you check in South Africa?

  1. List everything you take: prescription, over-the-counter, vitamins, herbs.
  2. Take the packs to a Dis-Chem or Clicks pharmacist or your clinic for a medicines review; this is usually free to ask.
  3. Include doses and the time of day you take each one.
  4. Update the list whenever something changes.
  5. Report suspected side effects to your doctor or pharmacist (see how to report a supplement side effect).

When should you see a doctor?

See a doctor urgently for unusual bruising or bleeding, black stools, palpitations, new muscle weakness, severe diarrhoea or confusion after starting a supplement. This is general information, not personal medical advice.

Sources

More in Healthy ageing

Educational information, not medical advice. Speak to a doctor, pharmacist or registered dietitian before using supplements if you are pregnant or breastfeeding, under 18, taking medication, or living with kidney, liver or heart disease. Prices were observed in October 2026 and are not offers.