Taking Diclofenac With Synthroid

In our latest question and answer, the pharmacist discusses taking diclofenac with Synthroid (levothyroxine).


Can I take diclofenac 100mg and Synthroid 150mcg at the same time or is it better to have a few hours between them? Thank you.

Asked by Mary On Apr 09, 2019

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Apr 09, 2019
Synthroid With Diclofenac


Diclofenac and Synthroid (levothyroxine) can be taken the same day, but you should separate their administration time since Synthroid is best absorbed on an empty stomach.

How To Take Synthroid

Synthroid is recommended to be taken on an empty stomach, usually first thing in the morning, at least 30 to 60 minutes before food or other medications for best absorption.[1]

Multiple studies show that the bioavailability (i.e. the rate and extent of absorption) of Synthroid is best when taken on an empty stomach. Taking it with food or other medications could potentially decrease the absorption of the medication, making it less effective.[2]

Some medications and supplements which are known to inhibit Synthroid absorption are even recommended to be taken at least 4 hours from Synthroid. These include:[3]

  • Calcium supplements
  • Fiber
  • Colesevelam
  • Iron supplements
  • Magnesium supplements
  • Antacids

Synthroid Absorption

If you can't take Synthroid in the morning, the best thing you can do is to take it consistently the same way every day.

The reason we are so concerned with how Synthroid should be taken is that it is considered a narrow therapeutic index drug. This means that there is a small margin between therapeutic, sub-therapeutic and toxic doses.[4]

Remember that Synthroid doses are measured in micrograms, which is 1/1000th of one milligram! We are talking very small doses here. Even slight changes in dose (or absorption) can have a significant impact on your thyroid hormone levels.

So, to reiterate, try and take Synthroid the same way every day, ideally in the morning and separated from food (including coffee and tea) as well as other medications.


Synthroid should ideally be taken by itself, in the morning, at least 30-60 minutes before food or other medications, such diclofenac. Some medications (e.g. antacids) need to be separated by at least 4 hours. This is to ensure optimal and consistent absorption of Synthroid.

  1. ^ Synthroid Prescribing Information
  2. ^ Clinical relevancy of the levothyroxine-continuous enteral nutrition interaction. PubMed
  3. ^ Conditions and drugs interfering with thyroxine absorption. PubMed (Subscription Required)
  4. ^ Draft Guidance on Levothyroxine Sodium FDA

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Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

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