Taking Levothyroxine And Linzess Together

In our latest question and answer, the pharmacist discusses the interaction between Linzess and Synthroid (levothyroxine).


I take Synthroid 50mcg every morning, and my doctor has also prescribed Linzess 145mcg to be taken every morning. Both medications instruct to be taken in the morning, 30 minutes before the first meal. I've come across information indicating potential interactions between these two medications. Is it safe to take them together, or would it be advisable to take one of these in the evening?

Asked by Bee On Aug 31, 2023

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Aug 31, 2023
Last updated Apr 18, 2024

Key points

  • Taking Synthroid (levothyroxine) and Linzess (linaclotide) separately is recommended due to potential absorption issues.

Quick Answer

It's advisable to take Synthroid (levothyroxine) and Linzess (linaclotide) separately due to potential absorption issues. Synthroid is generally recommended to be taken on an empty stomach in the morning, at least 30 minutes before food or other medications. Linzess is recommended to be taken 30 minutes before a meal as well, as studies show diarrhea is more likely to occur if taken with food (especially high-fat meals).

Detailed Answer

The concern with taking Synthroid and Linzess together is a decrease in Synthroid absorption, which could reduce how well the medication works.

Synthroid is a narrow therapeutic index drug, meaning that small changes in absorption or dose can have significant effects on its therapeutic efficacy.

Because of this, it's recommended to take Synthroid consistently on an empty stomach, 30 to 60 minutes before any food or other medications, to ensure optimal absorption.

Linzess, on the other hand, is used for the treatment of constipation and can cause diarrhea as a side effect. Diarrhea can potentially reduce the absorption of orally administered medications, including Synthroid.

Since Synthroid is recommended to be taken on an empty stomach before food and other medications, and because Linzess can cause diarrhea and reduce the absorption of oral medications, these drugs should generally not be taken at the same time.

How To Manage The Interaction

It is important to follow the administration instructions for each drug to ensure optimal effects, as well as reduced side effects.

You should work with your doctor or pharmacist to find the best times to take each drug for your specific medical situation. One example regimen could be:

  • Take Synthroid (levothyroxine) in the morning, 30 minutes before breakfast and other medications.
  • Take Linzess (linaclotide) on an empty stomach, at least 30 minutes before a meal (e.g., lunch) and apart from other medications.

I want to point out that although Linzess is recommended to be taken before the first meal, there is some flexibility here.

The following is from the prescribing information for Linzess:

Food Effect
In a cross-over study, 18 healthy subjects were given LINZESS 290 mcg for 7 days both in the non-fed and fed state. Neither linaclotide nor its active metabolite was detected in the plasma. Taking LINZESS immediately after the high-fat breakfast resulted in looser stools and a higher stool frequency compared with taking it in the fasted state [see Dosage and Administration (2.1, 2.2)]. In clinical trials, LINZESS was administered on an empty stomach, at least 30 minutes before breakfast.
Linzess Prescribing Information

The recommendation to take Linzess on an empty stomach is based on the fact that in clinical trials, when Linzess was given to test participants who had recently eaten, 'loose stools' as a side effect were seen more commonly when compared to those who took the drug on an empty stomach (as shown in the excerpt above).

So, realistically, the drug is generally safe to take at least 30 minutes prior to any meal, at approximately the same time each day. Taking it later in the day should not alter its overall effectiveness.

In my opinion, it is more important to take your Synthroid consistently in the morning before you've had any food or other medications to ensure consistent absorption.

If you are an early riser, you could certainly take Synthroid first thing when you wake up, wait 30 minutes to take Linzess, and then feel safe to consume food 30 minutes after that.

As everyone's medical situation is different, I certainly recommend speaking with your doctor about what is best for you.

Final Words

I hope you found this answer helpful!


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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