Taking Synthroid With Benefiber

In our latest question and answer, the pharmacist discusses the interaction between Synthroid and Benefiber.


I am on Synthroid and Nexium. Is there any issue with taking Benefiber? I read that Synthroid is affected by fiber, so is Benefiber bad to take when taking Synthroid? How long after I take my Synthroid (in the morning) can I take Benefiber?

Asked by MIKEK On Feb 10, 2019

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Feb 10, 2019
Benefiber Products On Shelf


You certainly should take your Synthroid (levothyroxine) and Benefiber (wheat dextrin) at separate times, and not together, to avoid an interaction.

Taking them together could result in decreased absorption of your Synthroid, potentially causing your thyroid levels to drop too low (i.e., hypothyroidism). Symptoms of hypothyroidism include:

  • Fatigue
  • Weakness
  • Shivering
  • Decreased metabolism
  • Brittle hair nails

If you ever notice any of the above symptoms, be sure to speak with your doctor about your therapy.

How To Take Synthroid

It is important to take Synthroid in a consistent manner, by itself on an empty stomach, most preferably in the morning. Taking it inconsistently, or with food, will make it difficult, if not impossible, to find the correct dose for you as your thyroid levels may fluctuate.

It is important to remember that doses of Synthroid are very low, and are measured in micrograms (1/1000 of a milligram). Even small changes to a dose make a significant impact and taking Synthroid with fiber will likely alter the amount you absorb.

The prescribing information for Synthroid states multiple times how it is best taken for optimal effects:

Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast.

Avoid Synthroid With Fiber

The prescribing information also explicitly warns against taking with drugs known to decrease absorption, such as fiber:

Consumption of certain foods may affect SYNTHROID absorption thereby necessitating adjustments in dosing. Soybean flour, cottonseed meal, walnuts, and dietary fiber may bind and decrease the absorption of SYNTHROID from the gastrointestinal tract. Grapefruit juice may delay the absorption of levothyroxine and reduce its bioavailability

When It Is Safe To Take Benefiber?

In regard when you can take Benefiber after Synthroid, recommendations vary.

Some sources recommend that you only need to wait 30 to 60 minutes, since, by that time, the Synthroid will most likely have been emptied from the stomach, into the gastrointestinal tract.

However, other sources are more conservative, including the prescribing information, which states that you should separate Synthroid from any drug or food known to affect absorption by at least 4 hours.

So, to be on the safe side, a 4-hour window may be best, but that can often be difficult to follow. It would be prudent to have a discussion with your doctor regarding how to best go about dosing Synthroid and Benefiber in a way that is most convenient for you.

The most important thing is to take your Synthroid the same way, every day.

Other Morning Medications With Synthroid

If you have other medications, you are supposed to take in the morning, like Nexium, that can complicate things.

We wrote an article recently discussing how to best approach these situations, which can be found here:

Final Words

Synthroid absorption is well known to be affected by many different drugs and food. It is essential to take the medication consistently to ensure optimal results and avoid fluctuations in your thyroid hormone levels.


Synthroid should not be taken with any fiber product, including Benefiber. Doing so can significantly affect the absorption of Synthroid. They should be separated by at least 4 hours.

  1. Synthroid Prescribing Information. AccessFDA
  2. Drug interactions with levothyroxine therapy in patients with hypothyroidism: observational study in general practice. 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

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