Levothyroxine and Calcium: What You Need to Know About This Common Drug Interaction

When you take levothyroxine, a synthetic form of the thyroid hormone T4 used to treat hypothyroidism, it needs to be absorbed properly in your gut to work. But if you take it at the same time as calcium, a mineral found in supplements, dairy, and fortified foods, your body can’t absorb the thyroid medication well. This isn’t a minor issue—it can mean your thyroid levels stay too low, leaving you tired, cold, and gaining weight even if you’re taking your pill every day.

It’s not just calcium. Iron, antacids, and even soy products can do the same thing. But calcium is one of the most common offenders because so many people take it for bone health, especially as they get older. The science is clear: calcium binds to levothyroxine in the digestive tract, blocking its absorption. Studies show that taking them together can drop levothyroxine absorption by up to 30%. That’s like taking half your dose and wondering why you don’t feel better.

Here’s what actually works: take levothyroxine on an empty stomach, at least 30 to 60 minutes before breakfast. Wait at least four hours after that before taking any calcium supplement. If you take calcium at night, that’s often the easiest fix—take your thyroid pill in the morning, and your calcium before bed. Same goes for iron, multivitamins with minerals, and even some antacids. Don’t just space them out—track it. Use a phone alarm or a pill organizer with time labels. Your thyroid doctor won’t know you’re taking calcium unless you tell them, and they can’t fix your levels if the medication isn’t being absorbed.

Some people think switching to a different brand of levothyroxine will solve the problem. It won’t. The issue isn’t the pill—it’s what’s in your stomach when you swallow it. Even if you take your thyroid med with water, if calcium is still in your gut from a snack or supplement, it’ll interfere. And no, drinking coffee with your pill doesn’t help either—caffeine can delay absorption too. Stick to plain water, empty stomach, and keep calcium away.

What about food? You don’t need to give up dairy forever. Just don’t eat it right after your pill. A bowl of yogurt at lunch? Fine. A glass of milk with breakfast 20 minutes after your pill? That’s a problem. The same goes for calcium-fortified orange juice or almond milk. Read labels. If it says "calcium added," treat it like a supplement.

If you’re on levothyroxine and still feel off, check your supplement list. Calcium is the usual suspect, but don’t forget iron pills, antacids with aluminum or magnesium, and even some fiber supplements. Your thyroid levels can look normal on paper, but if absorption is blocked, you’re still under-treated. That’s why many doctors recommend checking TSH levels 6 to 8 weeks after changing how or when you take your meds.

You’re not alone in this. Thousands of people take levothyroxine and calcium together without realizing the conflict. But once you know how to separate them, things click. Energy returns. Weight stabilizes. Brain fog lifts. It’s not complicated—just precise. And getting it right is one of the simplest, most effective things you can do for your thyroid health.

Below, you’ll find real advice from people who’ve been there—how to time their doses, what worked when nothing else did, and what mistakes to avoid. No fluff. Just what helps.