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    Ingredient guide · Ingredient reference

    Which supplements and medicines should not be taken together?

    There is no complete safe-or-unsafe list based only on supplement names. Exact ingredients, doses, medicines and health conditions determine the interaction. Some combinations need spacing, others need monitoring or avoidance, and separating them by a few hours does not remove every risk.

    Read the evidence ↓

    Supplement Science Insights Editorial Team

    Published September 23, 2026

    Separate an absorption interaction from a systemic one

    Calcium can reduce absorption of certain medicines, including levothyroxine and some antibiotics, for which product-specific timing matters. By contrast, changing the clock time does not necessarily prevent an interaction affecting drug metabolism or blood clotting. [1][2]

    Several combinations deserve particular review

    ODS identifies vitamin K with warfarin, St John’s wort with many medicines, and antioxidant supplements during some cancer treatments as examples. NCCIH warns that St John’s wort with certain antidepressants can cause serious serotonin-related effects. These are examples, not an exhaustive blacklist. [2][3]

    Supplement stacks can duplicate exposure

    Two products may contain the same vitamin, mineral or botanical under different marketing names. Add the amounts across a multivitamin, specialty blend and standalone capsule. A combined intake can be excessive even if each bottle is used according to its own serving instructions. [2]

    Review the complete list before changing prescriptions

    Imagine a person taking warfarin wants a greens powder and a new calming blend. Bring all labels and doses to the pharmacist or prescriber. Do not stop a prescribed medicine or assume a morning-versus-evening schedule makes the additions safe. [2][3]

    Hypothetical example — classify hypothetical combination problems
    DecisionUseful check
    Mineral binds a medicineSpecific spacing may help
    Drug metabolism changesSpacing may not solve it
    Duplicate ingredientsAdd total exposure
    Prescribed treatmentCoordinate changes
    Which supplements and medicines should not be taken together? — original article outline diagram
    Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

    Sources for this article

    1. Calcium - Health Professional Fact Sheet
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    2. Dietary Supplements: What You Need to Know - Consumer
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    3. St. John’s Wort: Usefulness and Safety | NCCIH
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.