Taking Doxycycline And Synthroid Together

In our latest question and answer, the pharmacist discusses the interaction between doxycycline and Synthroid.


Can you take Synthroid and doxycycline together at the same time each day since they both have similar nutrition, vitamin, and mineral restrictions?

Asked by Duck On May 14, 2024

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published May 16, 2024
Last updated Jun 14, 2024


Hello and thanks for sending in the great question!

You're correct that doxycycline and Synthroid have a similar warning regarding concurrent use with vitamin and mineral supplements. This warning is due to a potential decrease in absorption of Synthroid/doxycycline.

For instance, calcium carbonate can form an insoluble compound when combined with levothyroxine or doxycycline, while ferrous sulfate tends to form a complex with thyroxine. Both interactions can decrease the absorption of Synthroid and doxycycline, reducing their effectiveness.

Doxycycline isn't known to specifically interact with Synthroid, but Synthroid is generally recommended to be taken on an empty stomach and not with any other medications. This is explicitly stated in the prescribing information for the drug:

Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast.

Synthroid doses are incredibly low (it's dosed in micrograms), so any variation in absorption can make a big impact on your thyroid levels. Based on this, it is recommended to take the drug by itself, the same way every day, to ensure consistency.

If you have been prescribed to take Synthroid and doxycycline together, I recommend taking the Synthroid first thing in the morning and then taking doxycycline at least 30 minutes later.

In regard to taking doxycycline with food, although there is a warning about taking it with certain vitamins and minerals, immediate-release and delayed-release doxycycline tablets or capsules have the lowest tendency to bind with calcium ions among tetracycline type drugs (e.g., tetracycline, minocycline, doxycycline etc...). Based on this, according to FDA-approved labeling, doxycycline products can be taken with food to alleviate stomach irritation if it occurs, so the concern with decreased absorption isn't very significant. Per the prescribing information:

If gastric irritation occurs, doxycycline may be given with food or milk

Final Words

Thanks again for your question and feel free to reach back out anytime!


  • Synthroid Prescribing Information, AccessFDA
  • Doxycycline 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 [email protected]! You can also connect with Dr. Brian Staiger on LinkedIn.

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