Taking Probiotics With Synthroid

In our latest question and answer, the pharmacist discusses taking probiotics with the thyroid replacement medication Synthroid.


I am currently on Synthroid, which I take first thing in the morning. I have also started taking Phillips Colon Health probiotics for constipation. Can I take the probiotics an hour after the Synthroid when I eat breakfast, or will that impair the absorption of the Synthroid (as I know many supplements do)? Thanks.

Asked by Mike On Apr 07, 2019

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Apr 09, 2019
Synthroid With Probiotics With Capsules Image

Probiotic supplements should be safe to take the same day as Synthroid (levothyroxine). However, they should be taken at least 30 to 60 minutes after taking Synthroid to avoid negatively affecting the absorption of the drug.

The prescribing information for Synthroid, as well as most studies, recommend taking the drug by itself at least 30 to 60 minutes before food or other medications to allow it to absorb consistently.[1][2]

Taking it with other drugs or food can decrease absorption, potentially making the medication less effective, which could lead to symptoms of hypothyroidism (e.g. lethargy, weight gain, feeling of cold etc...).

It is even recommended to separate some drug by more than 60 minutes. These include:[3]

  • Fiber supplements
  • Antacids
  • Calcium supplements
  • Magnesium supplements

All of the above are recommended to be separated from Synthroid by at least four hours.

There have been no studies evaluating how probiotics could potentially affect Synthroid absorption if taken at the same time.

However, one study was completed where a probiotic supplement (VSL#3) was taken at least 2 hours after Synthroid. The study showed that, when compared to individuals that did not take the probiotic, there was no difference in thyroid-stimulating hormone (TSH), fT3 (free triiodothyronine), fT4 (free tetraiodothyronine) levels.[4]

So, as long as you separate your probiotic supplement from Synthroid by the appropriate amount of time (at least 30 to 60 minutes), you should be safe (although it should be noted that some studies suggest that our intestinal bacteria flora can affect thyroid hormone levels in general).[5]


There is no known interaction between Synthroid and probiotic supplements. Nevertheless, probiotics should be taken at least 30 to 60 minutes after taking Synthroid to avoid interference with absorption.

  1. ^ Synthroid Prescribing Information
  2. ^ Clinical relevancy of the levothyroxine-continuous enteral nutrition interaction. PubMed
  3. ^ Conditions and drugs interfering with thyroxine absorption. PubMed
  4. ^ Probiotics Ingestion Does Not Directly Affect Thyroid Hormonal Parameters in Hypothyroid Patients on Levothyroxine Treatment. PubMed
  5. ^ Link between hypothyroidism and small intestinal bacterial overgrowth. PubMed

About the Pharmacist

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

Recent Questions