Can I take these supplements together?
Pick two. You get a plain answer, the reason, how far apart to take them, and the sources it comes from.
Pair checker
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Better at different times: calcium may reduce iron absorption, so take calcium and iron supplements at separate times of day.
Why
In a study of 126 people, 300 to 600 mg of calcium added to a meal cut iron absorption by 50 to 60%, and it reduced heme iron absorption too. NIH ODS says the effect has not been definitively established, but experts suggest taking individual calcium and iron supplements at different times of the day.
Timing
Take iron in the morning and calcium with lunch or dinner, about 2 hours or more apart. A calcium and vitamin D combination tablet counts as calcium.
Sources
Check your whole list, not just one pair
Supplement Tracker checks every supplement you take against the others and reminds you of each dose at its own time.
Checked against NIH Office of Dietary Supplements, MedlinePlus, NCCIH, PubMed and Examine on November 10, 2026. The checker covers 52 pairs; a pair we have not checked says so instead of guessing.
Every pair we have checked
Check first: pairs with a medicine or a real risk
Ashwagandha + Thyroid medicine (levothyroxine)
Only with your doctor’s approval: NCCIH says ashwagandha might interact with thyroid hormone medicines and is not recommended for people with thyroid disorders.
Biotin + Thyroid medicine (levothyroxine)
Tell your doctor: high-dose biotin can make thyroid blood tests read falsely, which may affect how your levothyroxine dose is judged.
Calcium + Antibiotics (tetracyclines, quinolones)
Not at the same time: calcium has to be spaced from tetracyclines and ciprofloxacin, and the gap depends on the antibiotic.
Calcium + Thyroid medicine (levothyroxine)
Not at the same time: MedlinePlus says to take calcium carbonate at least 4 hours before or after levothyroxine.
CoQ10 + Blood thinner (warfarin)
Check with your doctor first: NIH sources say CoQ10 may interact with warfarin.
Fish oil (omega-3) + Blood thinner (warfarin)
Check with your doctor first: case reports describe INR rising when fish oil was added to warfarin or its dose was raised.
Iron + Antibiotics (tetracyclines, quinolones)
Not at the same time: iron has to be spaced from tetracyclines and ciprofloxacin, and the gap depends on the antibiotic.
Iron + Thyroid medicine (levothyroxine)
Not at the same time: MedlinePlus says to take ferrous sulfate at least 4 hours before or after levothyroxine.
Magnesium + Antibiotics (tetracyclines, quinolones)
Not at the same time: magnesium products have to be spaced from tetracyclines and ciprofloxacin, and the gap depends on the antibiotic.
Usually yes, they can share a dose, but check with a doctor first if you have kidney disease or take ACE inhibitors, ARBs or potassium-sparing diuretics.
Magnesium + Thyroid medicine (levothyroxine)
Ask your pharmacist: MedlinePlus lists antacids as possibly interacting with levothyroxine but gives no spacing for magnesium supplements.
Melatonin + Blood pressure medicine
Ask your doctor first: in a small trial, evening melatonin raised blood pressure in patients well controlled on nifedipine.
Probiotics + Antibiotics (tetracyclines, quinolones)
Usually yes: NCCIH says the combination appears safe for most people, but check first if you are very ill or your immune system is weak.
Selenium + Thyroid medicine (levothyroxine)
Probably, with your doctor’s approval: MedlinePlus does not list selenium among the products that interact with levothyroxine.
Vitamin K + Blood thinner (warfarin)
Only with your doctor’s approval: vitamin K can change how warfarin works, so your intake needs to stay consistent.
Zinc + Antibiotics (tetracyclines, quinolones)
Not at the same time: zinc has to be spaced from tetracycline and ciprofloxacin, and the gap depends on the antibiotic.
Fine, but take them at different times
Usually fine, but a calcium supplement taken with a meal can lower zinc absorption, so different meals is a simple precaution.
Better at different times: calcium may reduce iron absorption, so take calcium and iron supplements at separate times of day.
Yes, on the same day, but take them at different times: magnesium oxide and magnesium antacids may bind iron.
Better at different times: iron supplements of 25 mg or more taken with zinc can lower zinc absorption.
Fine in the same dose
Yes, you can take them together: no interaction between ashwagandha and iron is documented in NIH sources.
Yes. NIH lists no interaction between ashwagandha and magnesium, so taking them together, including at night, is fine for most people.
Ashwagandha + Melatonin
No interaction between ashwagandha and melatonin is documented in NIH sources, but both are used for sleep and may add drowsiness.
Biotin + Collagen
Yes. No documented interaction between biotin and collagen in NIH or Examine sources.
Yes, you can take them together: NIH sources document no absorption conflict between calcium and magnesium.
CoQ10 + Fish oil (omega-3)
Yes. No documented interaction between CoQ10 and fish oil in NIH or Examine sources.
Creatine + Caffeine (coffee, pre-workout)
Yes, many people combine them; studies do not show that caffeine universally cancels creatine, but results depend on the protocol.
Fish oil (omega-3) + Magnesium
Yes. NIH sources document no interaction between fish oil and magnesium, so they can be taken together.
Fish oil (omega-3) + Vitamin D
Yes. Fish oil and vitamin D can be taken together, ideally with a meal that contains some fat.
Yes, you can take iron and vitamin B12 together, even at the same time: no absorption conflict is documented.
Yes, take them together: vitamin C helps your body absorb nonheme iron, the form in most iron supplements and plant foods.
Yes, you can take them together: no study we found shows either one blocking the other’s absorption.
L-theanine + Magnesium
Yes. No documented interaction between L-theanine and magnesium in NIH or Examine sources.
Yes. NIH sources list no interaction between magnesium and melatonin, so you can take them on the same evening.
Yes, you can take them together: no study we found shows either mineral affecting the other’s absorption.
Yes. NIH sources document no interaction between magnesium and vitamin B12, so they can share a dose.
Yes. NIH sources document no absorption interaction between magnesium and vitamin C; just watch the dose of each.
Yes. Magnesium and vitamin D can be taken together: magnesium takes part in vitamin D metabolism rather than blocking it.
Yes, at typical doses you can take them together; only very high zinc, 142 mg a day, has been shown to impair magnesium absorption.
Yes, you can take them together: no absorption conflict between selenium and zinc is documented in NIH sources.
Turmeric (curcumin) + Fish oil (omega-3)
Yes. No documented interaction between turmeric and fish oil in NIH sources.
Probably yes: in a 2021 trial, 500 mg of curcumin taken with an iron supplement did not reduce iron absorption in healthy adults.
Vitamin B12 + Folate (folic acid)
Yes. B12 and folate can be taken together; keep folic acid within 1,000 mcg a day unless a doctor advises otherwise.
Vitamin C + Collagen
Yes. Vitamin C is needed to make collagen, and no harmful interaction is documented.
Vitamin C + Vitamin B12
Yes. The NIH B12 fact sheet lists no vitamin C interaction, and no source gives a timing gap for this pair.
Yes. NIH sources document no interaction between vitamin C and vitamin D, so they can go in the same dose.
Yes. Vitamin D and calcium work together: vitamin D is needed to absorb calcium from the gut.
Yes. NIH sources document no interaction between vitamin D and vitamin B12, so they can be taken together.
Yes, they can be taken together, but most people taking vitamin D do not automatically need added vitamin K.
Yes, they can be taken together, and many zinc products add copper. The risk is high-dose zinc over weeks lowering copper.
Yes, you can take them together: no absorption conflict between zinc and vitamin C is documented.
Yes, you can take them together: no absorption conflict between zinc and vitamin D is documented.
Questions
Which vitamins and minerals should not be taken at the same time?
The clearest conflicts are minerals that compete in the gut: iron with calcium, and iron or zinc at high doses. Calcium, iron, magnesium and zinc also need to be kept hours away from levothyroxine and from tetracycline and quinolone antibiotics. Most vitamins can share a dose.
What does the checker do with my choices?
Nothing leaves your browser except an anonymous count of which verdict was shown, and for supplement-only pairs which pair it was. No amounts, no medicines, nothing that identifies you.
What if my pair is not listed?
Then we have not checked it against sources yet and the checker says so rather than guessing. A pharmacist can check your exact products, including combination tablets.
More on the common conflicts: supplements you should not take together
This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician or qualified healthcare provider before starting any supplement regimen.