Multivitamin and medication: 12 interactions to know
Anticoagulants, antibiotics, statins, thyroid treatment: 12 interactions to absolutely know before stacking a multivitamin.
No dietary supplement is harmless in polytherapy. Here are the 12 most frequent interactions, to systematically validate with your pharmacist.
The major interactions to know involve vitamin K with VKA anticoagulants (changes the INR), iron and calcium with levothyroxine and certain antibiotics (space by 2 to 4 hours), and vitamin A with isotretinoin (risk of hypervitaminosis). In polytherapy, always have your multivitamin validated by your pharmacist before any prolonged use.
| Nutrient | Medication | What to do |
|---|---|---|
| Vitamin K | VKA anticoagulants (warfarin) | Medical advice - INR monitoring |
| Iron / Calcium | Levothyroxine | Space by at least 4 hours |
| Iron | Tetracycline / quinolone antibiotics | Space by at least 2 hours |
| Calcium | Bisphosphonates (Fosamax - Aclasta) | Space by at least 2 hours |
| Vitamin A | Isotretinoin (Roaccutane) | Avoid (risk of hypervitaminosis A) |
| High-dose vitamin B6 | Levodopa (Parkinson's) | Avoid mega-dose |
1. Vitamin K + VKA anticoagulants (warfarin)
Vitamin K antagonises the effect of VKAs. Any supplementation changes the INR. If you're on a VKA, talk to your doctor before any multivitamin containing K2 (our formula contains 75 µg).
2. High-dose vitamin E + anticoagulants
Additive effect on blood fluidity. High doses (>200 IU) to be avoided without advice.
3. Iron + levothyroxine
Iron chelates levothyroxine. Space the doses by at least 4 hours.
4. Calcium + levothyroxine
Same mechanism. Space by at least 4 hours.
5. Calcium + bisphosphonates
Calcium reduces the absorption of bisphosphonates. Space by at least 2 hours.
6. Iron + tetracycline / quinolone antibiotics
Iron chelates these antibiotics. Space by at least 2 hours.
7. High-dose vitamin B6 + levodopa
Reduces the efficacy of levodopa (Parkinson's). To be avoided in mega-dose.
8. High-dose vitamin C + chemotherapy
Possible interference with certain chemotherapies. Oncologist's advice essential.
9. Statins + high-dose niacin
Cumulative risk of myopathy. To be avoided in mega-dose.
10. Diuretics + magnesium / potassium
Depending on the diuretic class (potassium-sparing or not), risk of hyperkalaemia.
11. Multivitamin + isotretinoin
Isotretinoin is a vitamin A derivative. Stacking with a retinol-rich multi = risk of hypervitaminosis A.
12. Multivitamin + high-dose vitamin D treatment
Potential stacking on vitamin D. Check the total and adjust on medical advice.
Golden rule
Before any prolonged use of a multivitamin in polytherapy: photograph your bottle and send it to your pharmacist (or post to conseil@chutex-innovation.com). It takes 30 seconds and can avoid big mistakes.
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Public references and official sources
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Frequently asked questions
Can you take a multivitamin on anticoagulants?
With caution: vitamin K antagonises VKAs (warfarin) and changes the INR. If you're on a VKA, talk to your doctor before any multivitamin containing vitamin K2.
Should a multivitamin be spaced from thyroid treatment?
Yes: iron and calcium chelate levothyroxine and reduce its absorption. Space the doses by at least 4 hours. Same precaution with tetracycline and quinolone antibiotics (2 hours minimum).
How can I check my multivitamin's interactions?
Photograph your bottle and send it to your pharmacist before any prolonged use in polytherapy. It takes 30 seconds and rules out the major interactions (anticoagulants, thyroid, isotretinoin).