Take Iron with Thyroid Medication: What You Need to Know

When you take iron with thyroid medication, iron supplements can block the absorption of thyroid hormones like levothyroxine, making your treatment less effective. Also known as iron and levothyroxine interaction, this isn’t just a minor warning—it’s a common reason why people don’t feel better even when they’re taking their meds daily. If you’re on thyroid medication for hypothyroidism, you’re likely taking levothyroxine, and if you’re also taking iron for low iron levels or anemia, you’re probably not getting the full benefit from one or both drugs.

Levothyroxine, the synthetic form of thyroid hormone used to treat underactive thyroid, needs to be taken on an empty stomach for best absorption. But iron supplements, including ferrous sulfate, ferrous fumarate, or even multivitamins with iron, bind to it in your gut like glue. The result? Your body absorbs less thyroid hormone, your TSH levels stay high, and symptoms like fatigue, weight gain, and brain fog stick around. This isn’t theoretical—studies show iron can drop levothyroxine absorption by up to 50% if taken together. The same thing happens with calcium, magnesium, and even antacids. You don’t need to stop your iron. You just need to space it out.

The fix is simple: take your thyroid medication first thing in the morning, at least 30 to 60 minutes before eating or drinking anything besides water. Then wait at least four hours before taking iron. That’s long enough for your thyroid medicine to be absorbed before the iron shows up. Some people find it easier to take iron at bedtime, after dinner, as long as it’s been at least four hours since their thyroid pill. Don’t mix them in the same meal, don’t take them together in a pill organizer, and don’t assume your pharmacist already warned you—most don’t. This is one of those details that slips through the cracks.

If you’re on both meds and still feeling tired, bloated, or mentally foggy, this interaction could be why. Check your last blood test. If your TSH is still above target despite taking your thyroid pill regularly, iron might be the silent saboteur. Talk to your doctor about checking your ferritin levels. Low iron can mimic hypothyroid symptoms, so treating one without fixing the other just makes things worse. And don’t rely on herbal iron or food alone—your body needs consistent, bioavailable iron to support thyroid function, especially if you’re a woman, vegetarian, or have had gastric surgery.

There’s no magic formula, but timing matters. A few hours apart is all it takes to make your treatment work. You’re not doing anything wrong—you just need better timing. The posts below show real cases, practical tips, and comparisons of how other meds and supplements interact with thyroid drugs. You’ll find what works for people who’ve been where you are, without the fluff or guesswork.