Calcium binds certain medicines
Calcium is one of the most common supplement-medication timing issues, because it can bind drugs in the gut and reduce their absorption. NIH's calcium fact sheet lists several specific interactions [1].
Medications to separate calcium from
- Levothyroxine (thyroid medication). Calcium carbonate can interfere with absorption; take levothyroxine and calcium at least 4 hours apart [1] — see [supplements and thyroid medication](/learn/supplements-and-thyroid-medication).
- Quinolone antibiotics (ciprofloxacin, moxifloxacin, gemifloxacin). Take the antibiotic 2 hours before or after calcium [1].
- Dolutegravir (an HIV medication). Calcium can substantially lower its blood levels by binding it; the FDA advises taking dolutegravir 2 hours before or 6 hours after calcium [1].
- Lithium. Long-term lithium combined with calcium supplements could increase the risk of high blood calcium, so this combination warrants medical oversight [1].
The principle
Most of these are timing problems, not absolute contraindications: spacing the doses lets both the calcium and the medicine work. Dairy and calcium-fortified foods can contribute to the same binding, so they count too.
Practical guidance
- Take time-sensitive medicines (like levothyroxine) first, and save calcium for several hours later.
- Ask your pharmacist about the right gap for your specific medications, since the windows differ.
- Count dietary calcium (dairy, fortified foods) when timing matters, not just supplements.
- Don't stop prescribed calcium without checking — the goal is spacing (see [minerals that compete for absorption](/learn/minerals-that-compete-for-absorption)).