Search for supplement combinations and you will find charts claiming dozens of things cannot be taken together. Most of that is overstated. A small number of combinations genuinely compete for absorption, a smaller number matter medically, and the rest are fine.
Here is the honest version.
The combinations that actually matter
Iron and calcium
The best-documented pairing on this list. Calcium measurably reduces iron absorption, so a high-dose iron supplement and a high-dose calcium supplement should not be swallowed together. Leave two hours between them.
This also means iron with a large glass of milk, or with a calcium-fortified plant milk, is working against itself.
Iron and tea or coffee
Tannins and polyphenols in tea and coffee bind iron and reduce how much you absorb. If you are supplementing iron for a diagnosed deficiency, this one is worth taking seriously — leave an hour or two either side.
The reverse also helps: vitamin C substantially improves iron absorption. Taking iron with a glass of orange juice rather than tea is a genuinely free upgrade.
Zinc and copper
Sustained high-dose zinc can deplete copper over time, because they compete for the same transport route. Occasional zinc is fine; long-term high-dose zinc without copper is a real consideration worth raising with your GP.
Zinc and iron
Same story as iron and calcium. At high doses, separate them.
Thyroid medication and almost every mineral
This is the one to get right. Levothyroxine absorption is meaningfully reduced by calcium, iron and magnesium. Standard guidance is a four-hour gap, not two, and to take thyroid medication on an empty stomach.
If you take thyroid medication, do not take our word for the gap — confirm it with the pharmacist who dispenses it.
Antibiotics and minerals
Several antibiotic families bind to calcium, magnesium, iron and zinc, which reduces the antibiotic's effectiveness. That is a treatment failure risk, not an absorption inconvenience. Separate them by at least two hours and follow the dispensing advice on the box.
The medical ones — ask, don't guess
These are not about absorption. They are about effect, and they need a professional rather than an article:
- Omega-3 with blood thinners. Omega-3 has a mild antiplatelet effect. Relevant if you take anticoagulants or have surgery scheduled. Noted on our omega-3 page.
- Vitamin K with warfarin. Vitamin K directly opposes how warfarin works. Consistency matters more than avoidance — a conversation for your prescriber.
- Ashwagandha with thyroid or sedative medication. Flagged on our maca and ashwagandha page.
- DIM with hormonal medication or contraception. DIM influences oestrogen metabolism, so it belongs in a GP conversation. See our DIM page.
- St John's Wort with almost anything. It interacts with a long list of prescriptions including antidepressants and contraception. We do not stock it, and this is why.
Combinations people worry about unnecessarily
A multivitamin already contains iron, calcium, zinc and magnesium together. It has not been formulated by someone who missed the memo — the doses are modest enough that competition is not a practical problem. If you take Immuno 150, you do not need to split it into four doses.
Other pairings that are generally fine: omega-3 with almost anything; collagen with anything; NMN with your other supplements; vitamin D with magnesium; most botanical blends alongside vitamins.
Questions people ask
Is there a chart I can print?
The table in our supplement timing guide has a "keep apart from" column covering all of the above in one view.
What if I take a lot of different supplements?
Then the highest-value thing you can do is take your actual list — bottles or photos of the labels — to a pharmacist. They will check it against your prescriptions properly, and it costs nothing.
Can I just take everything at night to be safe?
No — that creates its own problems. Adaptogens and anything caffeinated belong earlier in the day, and iron on a full stomach absorbs poorly. Spreading a routine across morning and evening solves more than it causes.
Do these interactions apply to food too?
Some do. The iron-and-tea effect is a food effect. But food combinations rarely reach the doses where this matters — this is mostly a supplement-dose question.
The short version
Separate high-dose iron, calcium and zinc from each other. Keep minerals four hours from thyroid medication and two from antibiotics. Take anything that affects bleeding, hormones or mood past a professional. Everything else is very likely fine.
Who wrote this
Written by Daniel, founder of Nutritions Lab. We are a retailer, not a pharmacy. This page summarises well-established, widely published interaction guidance so it is in one place; it is not a substitute for a pharmacist reviewing your specific medication list, and we have said so at every point above where it matters.
Our approach to writing this kind of content is set out in our editorial policy. If we have something wrong here, tell us and we will fix it.
General information only, not medical advice. Supplements are not intended to diagnose, treat, cure or prevent any disease. Speak to your GP or pharmacist before combining supplements with prescription medication.