Levothyroxine and Calcium: What You Need to Know About Interactions

When you take levothyroxine, a synthetic thyroid hormone used to treat hypothyroidism. Also known as synthroid, it helps regulate your metabolism, energy, and body temperature. Many people don’t realize that taking it with calcium, a mineral found in dairy, supplements, and fortified foods. Also known as calcium carbonate, it’s commonly used for bone health and osteoporosis prevention. can block its absorption. This isn’t a minor issue—it can mean your thyroid levels stay low even if you’re taking your pill every day.

The problem is simple: calcium binds to levothyroxine in your gut, like a magnet grabbing a metal piece. That means your body can’t absorb the hormone properly. Studies show this interaction can drop levothyroxine absorption by up to 30%. That’s not a small drop—it’s enough to make your TSH levels climb again, leaving you tired, cold, or gaining weight without knowing why. The same thing happens with iron, antacids, and even some fiber supplements. You’re not imagining it. Your body is literally fighting the medicine.

So how do you fix it? Timing matters more than you think. Take levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast. Wait four full hours before taking any calcium supplement. That’s the sweet spot. If you take calcium at dinner, and levothyroxine in the morning, you’re safe. But if you pop a calcium pill with your morning coffee and cereal, you’re undoing your treatment. It’s not about skipping calcium—it’s about spacing it out. Your bones and your thyroid both need you to get this right.

And it’s not just supplements. Some antacids, soy milk, and even high-fiber foods can mess with absorption. If you’ve been taking your levothyroxine for years but still feel off, check your routine. Maybe your multivitamin has calcium. Maybe you started drinking almond milk. Maybe you switched to a different brand of thyroid pill. Small changes add up. Your doctor won’t always ask—so you need to track it yourself.

What you’ll find below are real, practical posts that dig into how levothyroxine interacts with other common meds, why timing isn’t just a suggestion, and how to spot when your thyroid treatment isn’t working because of something you’re taking with it. No fluff. Just what you need to make sure your medication actually works.