Calcium and your medicines: it is not what you eat, it is when
Calcium binds several drugs in the gut and stops them being absorbed at all. Levothyroxine (Synthroid) is the one that catches most people; tetracyclines (doxycycline, minocycline) and fluoroquinolones (ciprofloxacin, levofloxacin) are the others. The drug is not made weaker — it simply never gets in. Every number below is one ordinary serving, from USDA FoodData Central.
The part people get wrong
Nobody has to give up dairy. What matters is SPACING. Levothyroxine is taken on an empty stomach, and calcium — from food, a supplement, or an antacid — should be kept about four hours away from it. For ciprofloxacin the FDA label is specific: take it at least two hours BEFORE, or six hours AFTER, anything containing calcium, iron, magnesium or aluminium — the after-gap is the long one, and it is the one that gets missed. Levofloxacin and the tetracyclines run about two hours either side. The most common way this goes wrong is not a glass of milk: it is a calcium supplement or a Tums swallowed at the same time as the pill, which is the one thing to stop doing.
Calcium 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 | Calcium (mg) |
|---|---|---|
| Tofuraw, firm | 0.5 cup (126 g) | 861 |
| Cheeseparmesan, hard | 1 oz (28 g) | 336 |
| Milkwhole, 3.25% milkfat | 1 cup (244 g) | 277 |
| Collardscooked, boiled | 1 cup, chopped (190 g) | 268 |
| Spinachcooked, boiled | 1 cup (180 g) | 245 |
| Yogurtplain, low fat | 0.5 container (4 oz) (113 g) | 207 |
| Cheesecheddar, sharp | 1 slice (1 oz) (28 g) | 199 |
| Beanswhite, mature seeds | 1 cup (262 g) | 191 |
| Eggwhole, cooked | 1 cup, chopped (136 g) | 68 |
| Broccolicooked, boiled | 1 stalk, small (5" long) (140 g) | 56 |
| Kaleraw | 1 cup (21 g) | 53 |
| Orange juiceraw | 1 cup (248 g) | 27 |
| Breadwhole-wheat, prepared from recipe | 1 slice, regular (4" x 5" x 3/4") (46 g) | 15 |
The medicines this affects
Drugs in our catalog from the classes involved — tetracycline-class drug, quinolone antimicrobial and thyroxine. Each page carries that drug’s own FDA label.
Frequently asked questions
Which foods are highest in calcium?
Per serving, the highest on this list is tofu — 861 mg in 0.5 cup (126 g), per USDA FoodData Central. These are common foods rather than the absolute maximum in the USDA database: ranking every food by calcium 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 calcium if I take these medicines?
Nobody has to give up dairy. What matters is SPACING. Levothyroxine is taken on an empty stomach, and calcium — from food, a supplement, or an antacid — should be kept about four hours away from it. For ciprofloxacin the FDA label is specific: take it at least two hours BEFORE, or six hours AFTER, anything containing calcium, iron, magnesium or aluminium — the after-gap is the long one, and it is the one that gets missed. Levofloxacin and the tetracyclines run about two hours either side. The most common way this goes wrong is not a glass of milk: it is a calcium supplement or a Tums swallowed at the same time as the pill, which is the one thing to stop doing.
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 calcium" lists use, and they are misleading: nobody eats 100 g of dried thyme.
Sources
- Calcium — NIH Office of Dietary Supplements, Health Professional Fact Sheet ↗
- Levothyroxine Sodium tablet — FDA label, Drug Interactions (DailyMed) ↗
- CIPRO (ciprofloxacin) — 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.