Levothyroxine Interactions: What You Need to Know Before Taking It

When you take levothyroxine, a synthetic thyroid hormone used to treat hypothyroidism. Also known as Synthroid, it works best when your body can absorb it fully—something that’s easy to mess up with everyday foods, supplements, and other meds. If you’re not careful, your thyroid levels might stay out of whack, even if you’re taking your pill every day.

One of the biggest culprits? calcium, a mineral found in dairy, fortified juices, and supplements. Calcium supplements and even a glass of milk can bind to levothyroxine in your gut and stop it from getting into your bloodstream. Same goes for iron, often found in multivitamins or anemia treatments. Iron supplements act like a sponge for levothyroxine, leaving you with less of the hormone you need.

It’s not just minerals. antacids, like Tums or Pepcid, used for heartburn, and proton pump inhibitors such as omeprazole can also lower absorption. Even coffee, soy products, and high-fiber meals can interfere if taken at the same time. You don’t have to give up these things—just space them out. Take levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast, and wait four hours before taking calcium, iron, or antacids.

And it’s not just about timing. Some antibiotics like ciprofloxacin and doxycycline can also mess with levothyroxine absorption, which is why many people end up with weird thyroid symptoms after starting a new med. If you’re on multiple prescriptions, your pharmacist can spot these clashes before they cause trouble. Most drug interaction checkers miss the little things—like how your morning orange juice with added calcium could be quietly sabotaging your thyroid treatment.

People often think if they feel fine, their levothyroxine dose must be right. But thyroid levels don’t always match how you feel. A blood test is the only way to know for sure. If your TSH keeps creeping up despite taking your pill, the problem might not be your dose—it’s what you’re eating or taking with it.

What you’ll find below are real, practical breakdowns of the most common mistakes people make with levothyroxine. From dairy and calcium-fortified juices to how other meds like antibiotics and ADHD drugs play into the mix, these posts cut through the noise. No fluff. Just what works—and what doesn’t—based on how your body actually absorbs this medication.