When you take levothyroxine, a synthetic thyroid hormone used to treat hypothyroidism. Also known as Synthroid, it works by replacing the hormone your thyroid can’t make enough of. It’s simple—take it on an empty stomach, wait 30 to 60 minutes before eating, and you’re good to go. But here’s where things get messy: if you’re also taking calcium, a mineral commonly found in supplements, antacids, and fortified foods. Also known as calcium carbonate, it’s one of the most popular supplements in the world., you’re unknowingly blocking your own medication.
Calcium doesn’t just sit there. It binds to levothyroxine in your gut like glue, stopping your body from absorbing the hormone. That means your thyroid levels stay low even though you’re taking your pill. This isn’t theoretical—studies show calcium can cut levothyroxine absorption by up to 40%. And it’s not just calcium. Iron, magnesium, soy, and even coffee can do the same thing. If you’re taking a multivitamin with iron or an antacid with calcium carbonate after breakfast, you might as well be flushing your thyroid med down the toilet. The fix isn’t complicated: take levothyroxine first thing in the morning, wait at least four hours before taking any calcium supplement. If you take calcium at night, that’s fine—just keep it far away from your morning dose. Your doctor should check your TSH levels every 6 to 8 weeks after you start a new supplement. If your levels don’t improve, the problem might not be your dose—it’s what you’re taking with it.
People often don’t realize how many products contain calcium. Antacids like Tums? Calcium. Bone health supplements? Calcium. Some protein powders? Calcium. Even some oatmilks and orange juices are fortified with it. You don’t need to quit calcium—you just need to time it right. And if you’re on other meds like iron pills or proton pump inhibitors, those matter too. This isn’t about being perfect. It’s about being aware. The posts below dig into real cases where people thought their thyroid meds weren’t working, only to find out it was their morning smoothie or nightly calcium tablet. You’ll find guides on how to track your meds, what to ask your pharmacist, and why skipping a dose isn’t the answer when your levels are off. This isn’t guesswork. It’s a routine you can build—and stick to.
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