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Levothyroxine and Calcium

Levothyroxine (Synthroid) is a thyroid hormone replacement. Calcium supplements can bind to levothyroxine in the gut and prevent it from being absorbed properly.

Moderate interaction

Use with caution — ask your doctor or pharmacist.

What you need to know

Calcium forms an insoluble complex with levothyroxine in the digestive system, reducing how much thyroid hormone your body absorbs. Even calcium-fortified foods, antacids containing calcium, and dairy products can have a minor effect if consumed at the same time. The solution is simple: take levothyroxine on an empty stomach 30-60 minutes before food or any supplements.

What to do

Take levothyroxine first thing in the morning on an empty stomach with plain water.

Wait at least 30-60 minutes before eating or taking any supplements.

Take calcium supplements at least 4 hours after your levothyroxine dose.

When to call your doctor

Symptoms of underactive thyroid returning: fatigue, weight gain, feeling cold, constipation.

If your TSH level has changed without a dose adjustment.

Sources:FDANIH MedlinePlusAmerican Thyroid Association

DrugPair provides educational safety information only and is not a substitute for professional medical advice. Always ask a doctor or pharmacist before changing medicines, supplements, food, drinks, or prescription timing.

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