Can You Take Levothyroxine with Iron?
Last reviewed: · Source: US FDA drug label database
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Iron supplements bind to levothyroxine in the gut and reduce its absorption — separate them by at least 2-4 hours, ideally 4 hours.
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Is it safe to take Levothyroxine with Iron?
Iron is one of the most clinically important substances that interferes with levothyroxine absorption. Iron (and calcium, antacids) chelates levothyroxine in the gastrointestinal tract, forming insoluble complexes that cannot be absorbed. This can raise TSH and cause hypothyroid symptoms despite an unchanged levothyroxine dose. The solution is simple: separate the doses. Take levothyroxine on an empty stomach first thing in the morning, and take iron at a different time — at least 2 hours apart, ideally 4 hours.
How do Levothyroxine and Iron interact?
Ferrous and ferric ions form stable chelate complexes with thyroxine at physiological pH. Studies show iron reduces levothyroxine bioavailability by 40-50% when taken simultaneously. TSH rises within weeks of starting concurrent iron if spacing is not observed.
Data sourced from the US Food and Drug Administration (FDA) drug label database: OpenFDA levothyroxine label — iron and other divalent cation absorption interactions.
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Pregnant women (often prescribed both iron and levothyroxine — spacing is critical), people with iron-deficiency anaemia on hypothyroid treatment, anyone whose TSH has risen unexpectedly after starting iron supplementation.
For weight-based or dosage calculations, our dosage calculators can help. If you're tracking what you eat alongside your medication, 247CalorieCheck's food and nutrition checker is worth a look too.
What if I've already taken Levothyroxine and Iron?
Space them — levothyroxine first thing on empty stomach, iron later (with food, at least 2-4 hours after). Get TSH rechecked 6-8 weeks after changing the timing.
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Not sure if this combination is safe for your specific situation?
HealthLabs.com lets you check liver enzyme or kidney function levels before combining medications long-term — no GP referral needed.
Check your levels at HealthLabs →Always speak to your pharmacist or GP for personalised medical advice. Affiliate link — we may earn a commission.
Frequently Asked Questions
Can I take iron and levothyroxine together?
No — take them at least 2-4 hours apart. Iron binds levothyroxine in the gut, reducing its absorption by up to 50%.
How should I time levothyroxine and iron?
Levothyroxine: first thing in the morning on an empty stomach. Iron: with a meal, at least 2-4 hours later (e.g. lunchtime or evening).
Can iron tablets affect thyroid function?
Iron doesn't change thyroid function itself, but it reduces levothyroxine absorption — leading to higher TSH and returning hypothyroid symptoms if timing isn't managed.
I take iron in pregnancy and levothyroxine — is that OK?
Yes, but spacing is essential and TSH must be checked more frequently. Pregnancy already increases levothyroxine requirements; iron reducing absorption makes control harder.