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?
Aug 31, 2023- Synthroid should be taken on an empty stomach in the morning, at least 30 minutes before food or other medications, to ensure it works properly.
- Linzess can cause diarrhea which may reduce absorption of other medications like Synthroid, so these drugs should be taken at different times of day.
- You can take Synthroid first thing in the morning, wait 30 minutes, then take Linzess, and wait another 30 minutes before eating.
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 InformationThe 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!
References & sources
Glossary — Terms in This Answer
- Synthroid
- A brand name medication containing levothyroxine, used to treat an underactive thyroid gland.
- Levothyroxine
- A synthetic thyroid hormone medication that replaces or supplements the hormone your thyroid gland naturally produces.
- Linzess
- A brand name medication containing linaclotide, used to treat constipation.
- Linaclotide
- An active drug ingredient that works in the intestines to treat constipation and irritable bowel syndrome.
- Absorption
- The process by which a medication passes from your digestive system into your bloodstream.
- Narrow therapeutic index
- A characteristic of drugs where small changes in the amount absorbed or taken can significantly affect how well the medication works.
- Therapeutic efficacy
- How well a medication works to produce the desired healing or treatment effect.
- Diarrhea
- Loose or watery bowel movements that occur more frequently than normal.
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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