Spacing Supplements and Medicines: When Timing Matters
Why timing can matter when mineral supplements meet medicines such as levothyroxine, doxycycline, ciprofloxacin and alendronic acid, what NHS pages say, and why a pharmacist sets the gap.
Content last updated . This page has not been medically reviewed.
What "spacing" means
Spacing means leaving a gap between a medicine and a mineral product or mineral-rich food. The NHS gives the reason for ciprofloxacin: the calcium in dairy products and calcium-added drinks can stop your body from taking in all the medicine. [2] For alendronic acid it says the medicine works best on an empty stomach because the body can then absorb it properly. [3] This page uses NHS (UK) medicine pages as examples. They are not a complete list, the leaflet in your own box comes first, and other countries' labels can differ. For a wider table, see Mineral and medicine interactions: a reference table.Examples from official pages
| Medicine | What the NHS page says about minerals | Source |
|---|---|---|
| Levothyroxine (underactive thyroid) | Lists calcium and iron supplements, and antacids and other indigestion treatments, among things that may not mix well with it. Says to take it on an empty stomach 30 to 60 minutes before the first meal of the day. | [4] |
| Doxycycline (antibiotic) | Lists antacids and other indigestion treatments, and medicines or supplements that contain iron or zinc, among things that may not mix well with it. | [1] |
| Ciprofloxacin (antibiotic) | Says not to take it with dairy products or drinks with added calcium, and to leave a gap of at least 2 hours between them. | [2] |
| Alendronic acid (bone medicine) | Says not to take it with still or sparkling mineral water, tea, coffee, juice or milk, because these can reduce how much is absorbed. | [3] |
| Iron medicine (ferrous fumarate) | Lists doxycycline and ciprofloxacin, antacids, products containing magnesium, calcium, zinc or other iron, and levothyroxine as things that may affect how it works. | [5] |
The ciprofloxacin gap (2 hours) refers to dairy and calcium-added drinks on the NHS page we read. For levothyroxine, doxycycline, alendronic acid and iron medicine, the pages we read did not give a number of hours for mineral supplements, so a pharmacist is the right person to ask. A medicine page for one country or product does not decide the gap for another.
What a review says about levothyroxine
A 2021 systematic review that included 63 studies found limited evidence that coffee, soy products, fiber, and calcium or iron supplements all decreased levothyroxine absorption. [6] The authors wrote that keeping a proper time interval between levothyroxine and food intake, especially coffee, calcium or iron supplements, is an effective way to avoid these interactions. [6] The same review said effects of aluminium-containing preparations and chromium supplements need larger, better studies. [6] The NHS also says biotin (vitamin B7) can affect thyroid tests, which is a lab-test issue rather than an absorption issue. [4] See Thyroid problems and fatigue.Questions to bring to a pharmacist
- Which of my medicines, antacids, multivitamins and mineral products might affect each other?
- For the pairs that do, what gap does my leaflet or my pharmacist advise, and should it be fixed in my routine?
- Does my kidney, liver or thyroid condition, pregnancy, or age change the answer?
- Should I mention supplements before blood tests or surgery? See Supplements before surgery.
The NHS levothyroxine page also says to try to take it at the same time each day, which is one reason a steady routine helps. [4]
Where to read more
How interactions work, Interactions by drug class, Mineral interactions and absorption, Taking mineral supplements with food or on an empty stomach and Calcium.Frequently asked questions
How long should I leave between levothyroxine and calcium or iron?
The NHS page we read gives no number of hours for supplements. It lists calcium and iron supplements as things that may not mix well and says to take levothyroxine 30 to 60 minutes before the first meal of the day. Ask a pharmacist for the gap that suits your product. [4]
Can I take a multivitamin with an antibiotic?
Some antibiotics interact with minerals. The NHS lists iron or zinc supplements for doxycycline and advises a gap of at least 2 hours between ciprofloxacin and dairy or calcium-added drinks. Check your own combination with a pharmacist. [1][2]
Why can mineral water matter with a bone medicine?
The NHS says drinks including mineral water, tea, coffee, juice and milk can reduce how much alendronic acid is absorbed, and says to take it with tap water. [3]
Is the gap the same for every brand or form?
Not necessarily. Follow the leaflet for your own product and ask a pharmacist. The sources we read did not give gaps by product type.
Should I stop my supplement if I am unsure?
Do not stop or change a prescribed medicine on your own. Ask your pharmacist or prescriber how to time the supplement and the medicine.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: label instruction (what an official medicine page says) and review (a published systematic review).
Safety first
What we could not find
References
- NHS. Doxycycline (medicine page). NHS. Doxycycline (medicine page). Read 2026-10-23.
- NHS. Ciprofloxacin (medicine page). NHS. Ciprofloxacin (medicine page). Read 2026-10-23.
- NHS. How and when to take alendronic acid. NHS. How and when to take alendronic acid. Read 2026-10-23.
- NHS. Levothyroxine (medicine page). NHS. Levothyroxine (medicine page). Read 2026-10-23.
- NHS. Ferrous fumarate (medicine page). NHS. Ferrous fumarate (medicine page). Read 2026-10-23.
- Wiesner A et al. Levothyroxine Interactions with Food and Dietary Supplements: A Systematic Review. Pharmaceuticals (Basel). 2021. Wiesner A et al. Levothyroxine Interactions with Food and Dietary Supplements: A Systematic Review. Pharmaceuticals (Basel). 2021. Read 2026-10-23.