Can You Take Levothyroxine And Iron Supplements Together?

In our latest question and answer, the pharmacist discusses the interaction between levothyroxine and iron.


My doctor gave me a prescription to Ferrous Gluconate and Levothyroxine. I take 2 pills every other morning for Ferrous Gluconate. I take 1 pill every morning for levothyroxine. I read that they aren't supposed to be taken together. How should I take them?

Asked by Anna On May 24, 2023

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published May 26, 2023
Last updated Jun 03, 2023

Key points

  • Taking ferrous gluconate (iron supplement) with levothyroxine (thyroid medication) can reduce the absorption of levothyroxine, potentially compromising its effectiveness. It is advised to separate the administration of these medications by at least 4 hours to optimize the absorption of levothyroxine.


Thanks for reaching out! I can certainly provide you with information regarding the interaction between ferrous gluconate and levothyroxine, and how to properly take these medications.

Interaction Detail

ferrous Gguconate is a supplement that contains iron, while levothyroxine is a medication used to treat thyroid conditions.

Iron supplements, such as ferrous Gguconate, can interfere with the absorption of levothyroxine in the body and therefore, taking them together may reduce the effectiveness of the levothyroxine. This could negatively affect your thyroid levels.

Specifically, the iron ions in ferrous gluconate can bind to levothyroxine in the gastrointestinal tract, forming complexes that are poorly absorbed by the body. As a result, the bioavailability (rate and extent of absorption) of levothyroxine may be significantly reduced.

Levothyroxine requires optimal absorption to effectively regulate thyroid hormone levels in the body. When its absorption is compromised, there is a risk of inadequate thyroid hormone replacement, which can impact the management of thyroid conditions.

To ensure optimal absorption and effectiveness of your levothyroxine, it is recommended to separate the administration of these medications.

According to the prescribing information for Synthroid (a brand name for levothyroxine), it is advised to avoid taking levothyroxine tablets within 4 hours of iron and calcium supplements, as well as antacids. The prescribing information states this:

Inform patients that agents such as iron and calcium supplements and antacids can decrease the absorption of levothyroxine. Instruct patients not to take SYNTHROID [levothyroxine] tablets within 4 hours of these agents.

Additional Information

In general, levothyroxine is recommended to be taken by itself, first thing in the morning, separated by food and other medications by at least 30-60 minutes for optimal absorption. Some medications/supplements, like iron, should be separated by longer periods of time (4 hours as mentioned in the section above).

Making things a little tricky here is that iron supplements are also often recommended to be taken on an empty stomach for optimal absorption.

If you are going to be taking levothyroxine and iron on the same day, it would be best to try to work out a schedule where you can take both on an empty stomach, while separating them from each other by 4 or more hours.

Final Words

I hope this answer helped! Let me know if there is anything else I can answer for you.


  • Synthroid Prescribing Information, AccessFDA

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at! You can also connect with Dr. Brian Staiger on LinkedIn.

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