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?
May 14, 2024- Synthroid should be taken on an empty stomach first thing in the morning, at least 30 minutes before taking doxycycline, because Synthroid doses are very small and any change in absorption can affect your thyroid levels.
- Doxycycline can be taken with food if you experience stomach upset, even though there is a warning about certain vitamins and minerals, because doxycycline has a lower tendency to bind with calcium compared to other tetracycline antibiotics.
Answer
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 levothyroxine. 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!
References & sources
Glossary — Terms in This Answer
- Levothyroxine
- The active hormone in Synthroid that replaces or supplements thyroid hormone in the body.
- Absorption
- The process by which a medication passes through the digestive system into the bloodstream to become active in the body.
- Insoluble compound
- A substance that cannot dissolve in liquid, which prevents the body from absorbing it.
- Micrograms
- Very small units of measurement; one microgram is one millionth of a gram.
- Thyroid levels
- The amount of thyroid hormone circulating in the bloodstream.
- Tetracycline
- A class of antibiotic drugs that includes doxycycline and has similar properties and interactions.
- Gastric irritation
- Stomach discomfort or inflammation caused by a medication.
- Prescribing information
- Official FDA-approved instructions from the drug manufacturer about how to safely use a medication.
Dr. Brian Staiger, PharmD
Doctor of Pharmacy, board certified clinical pharmacist (BCPS), American Herbalist Guild, Medication Therapy Management certified
Brian Staiger, PharmD, BCPS, is a licensed pharmacist with more than 13 years of experience across retail pharmacy, clinical pharmacy, medication safety, pharmacy program development, and healthcare administration. He is the founder of HelloPharmacist.com, where he helps patients...
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