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