VITAMINS & SUPPLEMENTS · GUIDE
Formulas and Medicine Interactions: Reference by Ingredient and Drug Class
A reference table of documented supplement and medicine interactions drawn from the NHS, FDA and MedlinePlus, with a clear note on what these sources do not cover.
Content last updated . This page has not been medically reviewed.
Back to Supplement FormulasQuick answer
Some vitamins, minerals and herbs change how medicines work, and some medicines change how the body handles a nutrient. This page collects interactions that official sources we read actually name, organized by ingredient and medicine. It is not complete. If a medicine you take is not listed, that does not mean there is no interaction. Ask a pharmacist, and never stop or change a prescribed medicine on your own.
How interactions happen
The FDA says certain dietary supplements can change absorption, metabolism or excretion of a medication, which can leave you with too much or too little of the medicine. [1] Formulas make this harder to track because one product can hold many ingredients. Reading each ingredient on the label is the first step: see how to evaluate a supplement formula.Interactions named in the sources we read
Evidence label: "official advice" means a health body's published guidance, not a trial we reviewed.| Ingredient in a supplement or formula | Medicine or test | What the source says | Strength |
|---|---|---|---|
| Vitamin K supplements | Warfarin (blood thinner) | The NHS says not to take vitamin K supplements while on warfarin [2] | Official advice (UK) |
| Foods high in vitamin K | Warfarin | The NHS says foods such as broccoli, spinach and other leafy greens can affect how warfarin works, and to talk to the warfarin clinic [2] | Official advice (UK) |
| Vitamin E | Warfarin, aspirin, ginkgo | The FDA says all of these can thin the blood, and taking them together may raise the chance of internal bleeding or stroke [1] | Official advice (US) |
| Calcium and iron supplements | Levothyroxine (thyroid medicine) | The NHS lists them among supplements that may not mix well with levothyroxine [3] | Official advice (UK) |
| Biotin (vitamin B7) | Thyroid blood tests | The NHS says biotin can affect thyroid tests [3] | Official advice (UK) |
| St. John's wort (herb sometimes added to mood blends) | Medicines for HIV/AIDS, heart disease, depression, organ transplants; birth control pills | The FDA says these are less effective when taken with St. John's wort [1] | Official advice (US) |
| Potassium pills and "herbal or dietary supplements" | ACE inhibitors (blood pressure and kidney medicines) | MedlinePlus tells patients to tell their provider about potassium pills and herbal or dietary supplements; it names what to report, not a specific interaction [4] | Official advice (US) |
| High-dose folic acid (above 1 mg) | Vitamin B12 deficiency (not a medicine) | The NHS says it can mask the symptoms of B12 deficiency [5] | Official advice (UK) |
| High-dose zinc | Copper levels (not a medicine) | The NHS says high zinc reduces the copper the body can absorb [6] | Official advice (UK) |
For multivitamins specifically, see multivitamins and medicine interactions.
What we could not find
Proper evidence not found for a complete drug-class table. We searched NHS medicine pages for warfarin and levothyroxine, the FDA consumer update on mixing medications and supplements, NCCIH's supplement pages and the MedlinePlus ACE inhibitor page. They do not list interactions for many drug classes, such as diabetes medicines, cholesterol medicines, antibiotics, anti-seizure medicines or immune-suppressing medicines. For those, ask a pharmacist. The site's interactions by drug class and medication interactions pages go further for botanicals; St. John's wort interactions has its own page.Who is more likely to be affected
- People on several medicines. Each added product adds chances for an interaction.
- People with kidney disease. NIDDK explains that when kidneys filter less, medicines can build up unsafely in the blood, so the pharmacist and care team need to know about all medicines, vitamins and supplements. [7]
- People planning surgery. The FDA notes that supplements can interact in harmful ways with medicines needed before, during or after surgery. [1]
- Children, and people who are pregnant or breastfeeding. The FDA says children could be harmed by taking both supplements and medicines, and that pregnant or breastfeeding women should discuss any supplement with a health care professional. [1]
What to do with this page
Take your complete list of medicines and supplements, including the amounts, to a pharmacist. The FDA recommends bringing a list of everything you take to each visit. [1] If a label includes botanical ingredients, check those too. A product's label may not match its contents, according to NCCIH. [8]Frequently asked questions
Does vitamin K interact with warfarin?
Yes. The NHS says not to take vitamin K supplements while taking warfarin, and that foods high in vitamin K can affect how warfarin works. [2] See also the vitamin K page.
Can calcium or iron affect thyroid medicine?
The NHS lists calcium and iron supplements among the products that may not mix well with levothyroxine. Ask a pharmacist about your own situation. [3]
Does vitamin E thin the blood?
The FDA lists vitamin E among products that can thin the blood and says that taking it with warfarin, aspirin or ginkgo may increase the chance of internal bleeding or stroke. [1]
Does biotin affect lab tests?
The NHS says biotin can affect thyroid tests. [3] See biotin for hair, skin and lab-test details.
Where can I check a specific medicine?
Ask a pharmacist, who can review your whole list. The FDA advises talking to a doctor, pharmacist or other health care professional before using a supplement. [9]
References
- FDA: Mixing Medications and Dietary Supplements Can Endanger Your Health (content current 2 June 2022). Read 2026-10-23.
- NHS: Warfarin, medicine used to prevent and treat blood clots (page last reviewed 24 February 2026). Read 2026-10-23.
- NHS: Levothyroxine, a medicine for an underactive thyroid (page last reviewed 6 July 2026). Read 2026-10-23.
- MedlinePlus: ACE inhibitors. Read 2026-10-23.
- NHS: Vitamins and minerals, B vitamins and folic acid (page last reviewed 3 August 2020). Read 2026-10-23.
- NHS: Vitamins and minerals, Others (zinc, selenium, magnesium, manganese, beta-carotene; page last reviewed 3 August 2020). Read 2026-10-23.
- NIDDK: Managing Chronic Kidney Disease (last reviewed October 2016). Read 2026-10-23.
- NCCIH: Using Dietary Supplements Wisely (last updated January 2019). Read 2026-10-23.
- FDA: Information for Consumers on Using Dietary Supplements (content current 21 October 2022). Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.