Is Synthroid Gluten-Free? Hidden Fillers, Dyes, and Ingredients

Is Synthroid Gluten-Free?

Are you actively trying to avoid gluten-containing foods? Do you also have hypothyroidism?

If so, then this article is perfect for you. 

I’m going to jump the gun and tell you that Synthroid is indeed gluten-free, but it may contain other ingredients that can cause issues. 

We are going to discuss the gluten content of the thyroid medication Synthroid and discuss various reasons why you may not be tolerating your thyroid medication which may help explain why you are still suffering from certain symptoms. 

Let’s jump in: 

Thyroid Medication and Gluten – Why Does it Matter?

Why does it matter if your thyroid medication is gluten-free?

The answer is actually quite simple. 

It’s only necessary to take thyroid medication if you have a condition known as hypothyroidism. 

And the condition of hypothyroidism is most often caused by the autoimmune disease Hashimoto’s thyroiditis (1). 

The problem is that if you have one autoimmune disease, you are much more likely to develop another. 

And studies have shown that up to 5% of people with Hashimoto’s also have Celiac disease (2).

And, as you probably know, Celiac disease is an autoimmune disease in which your body reacts negatively to gluten (3) (from any source). 

And, in a nutshell, that’s why avoiding gluten is so important if you have thyroid disease!

It turns out that about 70-90% of people with hypothyroidism probably have thyroid disease due to an autoimmune condition

Does that mean that this information matters to you?

Not necessarily, but it’s still worth looking into because, as we just discussed, many patients with hypothyroidism should be avoiding gluten. 

But, even if you do tolerate gluten-containing products, you still may want to avoid levothyroxine and Synthroid formulations because they contain other ingredients that may cause issues (we will talk more about that below). 


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Gluten Content of Synthroid

So, to answer the question of whether or not Synthroid is gluten-free, we can take a look at a recent study (4) that attempted to answer that exact question. 

This study, while it was funded by the makers of Synthroid, still contains valuable information that we can use. 

The result of the study was this:

They found that Synthroid contains less than 3.0 parts per million of gluten in all of the various ingredients that are used to make the Synthroid medication. 

The standard concentration to consider food gluten-free is anything less than 20 parts per million, so by food standards, you can safely consider Synthroid to be gluten-free. 

As you can see from the image above, the researchers were able to break down the individual ingredients of Synthroid to test each batch to see if they were gluten-free. 

This is important because the components used to make Synthroid come from different locations before they are all put together. 

The manufacturing of these ingredients isn’t necessarily standardized, but we can conclude from these results that the batches that were tested were indeed gluten-free. 

In addition to gluten, the researchers also evaluated Synthroid for aluminum. 

They found that Synthroid contains a minimal amount of aluminum, but not enough to cause concern for the majority of people. 

Reasons you May not Tolerate Synthroid (Beyond Gluten)

But, just because it doesn’t contain gluten, does that mean it will work for you?

And the answer to that is not necessarily. 

There are a variety of other reasons why you may not be reacting as well as you’d like to Synthroid and we are going to explore those reasons below. 

Let’s take a look at the ingredient list one more time: 

From this list, you can see a number of ingredients that are known as excipients. 

These excipients are the ingredients used to make medications take their shape, protect them from degradation in the intestinal tract, give them coloring, and help support the active medication. 

All medications contain excipients, but not all medications contain the exact same excipients. 

The problem is that the excipients in medications (any type of medication) have been known to cause problems and may be a source of reaction for many people (5). 

Below, I’ve taken the most common excipients and I’ve gone over the reasons you may be reacting to them. 

#1. Lactose monohydrate

Lactose monohydrate (6) is a fairly obvious one and is found in every formulation of Synthroid currently available (this includes all of the various dosages). 

Lactose, as the name implies, is a sugar molecule and one that many people react negatively to. 

If you are lactose intolerant, and you take Synthroid, then you may be reacting to the lactose found in this medication. 

How do you know if you are reacting to it?

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The majority of people who suffer from lactose intolerance react with symptoms including gastrointestinal distress, bloating, cramping, gas, and nausea. 

If you experience these side effects after taking Synthroid then it may be due to this inactive ingredient. 

It is estimated that up to 65% of people in the United States have problems breaking down lactose

When you combine this with the fact that Synthroid is the #1 most prescribed medication, you can see where this might be a problem! 

#2. Fillers/dyes/additives

Another reason you may be reacting negatively to Synthroid may have to do with the fillers, dyes, colorings, and binders inside of the medication. 

These ingredients are all there to create the look and feel of thyroid medication and to help it be more stable in the GI tract. 

One of the biggest problems with these ingredients, though, is that they can actually limit the absorption of the medication. 

In fact, newer studies have shown that medications with fewer ingredients tend to be better absorbed compared to medications that have more ingredients. 

And, because of these ingredients, doctors usually recommend that you take your thyroid medication on an empty stomach and away from food and drink. 

But, again, newer studies have shown that you can actually take thyroid medication (such as Tirosint) with food and drink and still absorb your medication without any issues. 

#3. The bioequivalence of Synthroid is not equal to Levothyroxine and Vice versa

Last but certainly not least, is the fact that Synthroid and levothyroxine are not considered to be bioequivalent. 

What does that mean?

It means that even though these medications both contain thyroxine (the T4 thyroid hormone), they are not treated in the same way inside your body. 

So, if you are experiencing symptoms despite taking enough medication to normalize your TSH, it may have more to do with your medication name and not the dose you are taking. 

If you fit into this category, then switching your medication from Synthroid to levothyroxine (or vice versa) may actually improve your situation. 

What to do Next?

How do you know if you need to make any changes to your medication?

One of the easiest ways to know is if you still remain symptomatic with hypothyroid symptoms, despite taking ‘enough’ thyroid medication. 

We aren’t going to get into your thyroid dose (you can read more about that here), but just realize that your dose may play a very important role in how you are feeling. 

If you still have fatigue, depression, weight gain, cold hands/feet, hair loss, etc. while taking your medication then you may be reacting to the ingredients we’ve discussed above. 

If you fit into that category there are a few things that you can consider: 

  • #1. Switch to the 50mcg dose of Synthroid or Levothyroxine – The 50mcg dose of Synthroid/levothyroxine contains the fewest inactive ingredients out of all thyroid medications. Switching your dose of thyroid medication to the 50mcg tablet may help. 
  • #2. Consider switching to Tirosint – Perhaps the best option is to switch to a newer thyroid medication known as Tirosint. Tirosint contains only 4 total ingredients (3 inactive and 1 active) and is formulated as a liquid (7). Because of this, it’s highly absorbed, can be taken with food (8), still works even if you are taking acid-blocking medications (9), and so on. I find that most patients do quite well when switching to Tirosint over other medications. 
  • #3. Switch to NDT or other thyroid formulations – Another option is to switch from Synthroid to another class of thyroid medications known as Natural Desiccated Thyroid hormones. These medications don’t contain as many inactive ingredients and also contain other thyroid medications (T2, T3, and T4) in addition to calcitonin. 


The bottom line?

Synthroid can and should be considered a gluten-free medication because it contains less than 3 ppm (parts per million) of gluten. 

But, even though it is gluten-free, doesn’t mean it’s a perfect medication. 

Many people may still negatively react to inactive binders, fillers, dyes, lubricants, and even ingredients such as lactose. 

If you are having trouble tolerating Synthroid and you are still experiencing negative symptoms, then it may be worth considering a change to another type of thyroid medication

Now I want to hear from you:

Are you using Synthroid?

Do you feel it’s working for you?

Are you also gluten-free?

Do you think you need to switch medications?

Leave your questions or comments below! 










are thyroid medications gluten free?

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About Dr. Westin Childs

Hey! I'm Westin Childs D.O. (former Osteopathic Physician). I don't practice medicine anymore and instead specialize in helping people like YOU who have thyroid problems, hormone imbalances, and weight loss resistance. I love to write and share what I've learned over the years. I also happen to formulate the best supplements on the market (well, at least in my opinion!) and I'm proud to say that over 80,000+ people have used them over the last 7 years. You can read more about my own personal health journey and why I am so passionate about what I do.

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