Magnesium and your medicines: the antacid that stops your antibiotic from working
Magnesium binds several drugs in the gut and blocks their absorption — the same chelation trap as calcium and iron. It hits the tetracyclines (doxycycline, minocycline), the fluoroquinolones (ciprofloxacin, levofloxacin), the oral bisphosphonates (alendronate, risedronate) and levothyroxine. The drug is not made weaker — it simply never gets absorbed. Every number below is one ordinary serving, from USDA FoodData Central.
The part people get wrong
Food magnesium is rarely the problem; a magnesium-containing ANTACID or laxative is. Milk of Magnesia, Maalox, Mylanta, Rolaids and many 'calcium-magnesium' supplements are concentrated magnesium — swallow one at the same time as your antibiotic and you can cancel the dose. Per the ciprofloxacin FDA label, take the fluoroquinolone at least two hours BEFORE, or six hours AFTER, anything with magnesium, calcium, iron or aluminium; the tetracyclines run about two hours either side; oral bisphosphonates and levothyroxine want a clear empty-stomach window of their own. Separate them in time and you keep both.
Magnesium in common foods — per serving, not per 100 g
Values from USDA FoodData Central for the serving shown. These are foods people actually eat: ranking the whole USDA database by density would put dried thyme and defatted soy flour at the top, which is accurate and no use to anyone.
| Food | Serving | Magnesium (mg) |
|---|---|---|
| Pumpkin seedsroasted | 1 oz (28 g) | 156 |
| Spinachcooked, boiled | 1 cup (180 g) | 157 |
| Black beansmature seeds, cooked | 1 cup (172 g) | 120 |
| Brown ricelong-grain, cooked | 1 cup (195 g) | 86 |
| Almondsdry roasted | 1 oz (23 nuts) (28 g) | 80 |
| Cashewsdry roasted | 1 oz (28 g) | 74 |
| Dark chocolate70-85% cacao | 1 oz (28 g) | 64 |
| Edamameshelled, cooked | 0.5 cup (78 g) | 50 |
| Peanut buttersmooth | 2 tbsp (32 g) | 49 |
| Avocadosraw, all commercial varieties | 1 cup, sliced (146 g) | 44 |
| Yogurtplain, low fat | 1 container (8 oz) (227 g) | 42 |
| Bananaraw | 1 medium (118 g) | 32 |
The medicines this affects
Drugs in our catalog from the classes involved — tetracycline-class drug, quinolone antimicrobial and bisphosphonate. Each page carries that drug’s own FDA label.
Frequently asked questions
Which foods are highest in magnesium?
Per serving, the highest on this list is pumpkin seeds — 156 mg in 1 oz (28 g), per USDA FoodData Central. These are common foods rather than the absolute maximum in the USDA database: ranking every food by magnesium density puts dried herbs and defatted soy flour at the top, which is true and useless to someone deciding what to have for dinner.
Do I need to avoid magnesium if I take these medicines?
Food magnesium is rarely the problem; a magnesium-containing ANTACID or laxative is. Milk of Magnesia, Maalox, Mylanta, Rolaids and many 'calcium-magnesium' supplements are concentrated magnesium — swallow one at the same time as your antibiotic and you can cancel the dose. Per the ciprofloxacin FDA label, take the fluoroquinolone at least two hours BEFORE, or six hours AFTER, anything with magnesium, calcium, iron or aluminium; the tetracyclines run about two hours either side; oral bisphosphonates and levothyroxine want a clear empty-stomach window of their own. Separate them in time and you keep both.
Where do these numbers come from?
USDA FoodData Central (SR Legacy), for the household serving shown next to each food — not per 100 g. Per-100-g figures are what most "foods high in magnesium" lists use, and they are misleading: nobody eats 100 g of dried thyme.
Sources
- Magnesium — NIH Office of Dietary Supplements, Health Professional Fact Sheet ↗
- CIPRO (ciprofloxacin) — FDA label, Drug Interactions (DailyMed) ↗
- Doxycycline — FDA label, Drug Interactions (DailyMed) ↗
- USDA FoodData Central, SR Legacy ↗
Nutrient values are USDA reference data for the serving shown and vary with variety, growing conditions and cooking. This page is general information, not medical advice — never change your diet or your dose on the strength of a web page. Talk to whoever manages your treatment.