The core issue: minerals bind antibiotics
Some antibiotics form insoluble complexes with metal minerals, so taking them together means you absorb less of the drug — potentially making the antibiotic less effective. This is a timing problem with a simple fix [1].
Antibiotics most affected
- Tetracyclines (doxycycline, minocycline)
- Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin)
These bind to calcium, magnesium, iron, zinc, and aluminum, so mineral supplements, antacids, and even mineral-fortified products can interfere [1][2].
How to space them
NIH's guidance for magnesium-containing supplements is to take them at least 2 hours before, or 4 to 6 hours after, these antibiotics [1]. The same separate-by-hours principle applies to calcium, iron, and zinc. For calcium specifically, NIH advises taking quinolone antibiotics 2 hours before or after calcium [2].
Other supplement-antibiotic considerations
- Probiotics are sometimes taken to offset antibiotic-related digestive upset; if you do, separating them from the antibiotic dose is reasonable, and your clinician can advise.
- St. John's wort and other interacting herbs can affect drug levels broadly (see [herb-drug interactions](/learn/herb-drug-interactions-overview)).
- Dairy and mineral-fortified foods count too, since the calcium causes the same binding.
Practical guidance
- Separate mineral supplements (calcium, magnesium, iron, zinc) and antacids from tetracyclines and fluoroquinolones by the hours above.
- Take the full antibiotic course as prescribed, and don't skip doses to fit supplements — adjust the supplement timing instead.
- Tell your prescriber and pharmacist what supplements you take when starting an antibiotic.