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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16 thoughts on “Is Synthroid Gluten-Free?”

  1. Dr. Childs,
    I’m curious as what you think of skin issues, (eczema, atopic dermatis, psoriasis) and Levothroxine.

  2. In 2020 my health plan will no longer cover my Synthroid. They want me to switch to Levothyroxine, Levoxyl or Unithroid. Long story short. I have been Paleo/gluten free for 4 years. I also have MS so I try to avoid aluminum binders. AND it has taken me two years to get my TSH under control. I am running perfectly on Synthroid and I do not want to take a chance and switch. (but) reading about Tirosint has interested me. Not sure if it is generic?
    What do you suggest? Thanks

    • Hi Shelly,

      There is no generic for Tirosint. If you like Synthroid you can always opt for the cash price. It’s probably not as expensive as you would think and your insurance can’t force you to take a medication if you don’t want to. If you have a prescription you can work out a price with the pharmacy.

  3. Dr. Childs,

    I recently had my thyroid removed…..thought it was precancerous nodules, but ended up being Hashimoto’s. I also have Celiac Disease. Before my surgery I was placed on Levothroxine (25 mcg). I started having oral issues….pain, swelling and gums hurt every time I ate. My doctor had me stop taking it and my symptoms improved until my thyroid was removed and I got back on the Levothroxine (now I take 2 50 mcg per day for a total of 100 mcg). Now my symptoms have returned. My endocrinologist put me on the 50 mcg, which are white and she thought maybe the dye was bothering me. I guess my question is, have you heard of anyone having oral reactions to thyroid medicine or am I just weird? I also am lactose intolerant. At this point I am at a loss and don’t know what to do unless I’ve just developed an allergy to something else all of a sudden and it’s just a coincidence. Any help is greatly appreciated!

    • Hi Amy,

      Yes, all the time 🙂 Just to give you an idea of how clueless doctors are (including endocrinologists) both levothyroxine and Synthroid contain lactose monohydrate which, as you guessed it, contain lactose. Levoxyl is an alternative that does not contain lactose and Tirosint is even better. You can read more here:

  4. I’ve been gluten free for about 8 years, and before that I was diagnosed with Hypothyroidism. Synthroid was the medicine that made my numbers right, but I still dealt with symptoms. I would regularly ask to get my blood tested just to make sure nothing changed.

    Recently, started trying gluten again, and the fatigue and clouded mind was not good. I stopped having it again after two weeks, but I’m still dealing with issues. Not sure if gluten could still be affecting my thyroid and the way the medicine was working before?

    I’ve worked with a alternative health nutritionist before and my aluminum levels were high. I wonder after reading your article if it could be because of my medicine.

  5. Hello Dr. Childs,
    I had thyroid surgery several years ago (1/2 of it removed) and after 2 years was placed on Synthroid. I’ve found that the medication is inconsistent in that it -at first, helped with the depression and it improved the TSH levels, but I still have terribly dry skin, occasional canker sores, fatigue. I’m considering a switch to the Tirosint-is the dosage the same as Synthroid, ie starting with 50mcg & up?

  6. I am on Levothyroxine and suffer from all the side effects that you listed above. Weight gain, hair, loss, depression, mood, swings, terrible, joint pains, and etc. I had my thyroid removed eight years ago, and the doctor said I had Hashimoto. My endocrinologist will not order any test results except TSH. She said once the thyroid is removed, you no longer have Hashimoto. I would like to try Synthroid and see if that would work better, or one of the other thyroid medicines.

    • Hi Elizabeth,

      It would certainly be worth a try if you aren’t doing well on levothyroxine. But, just so you are aware, there are lots of other options that are usually tolerated much better than even Synthroid. Medications like Tirosint, Cytomel, liothyronine, and NDT can all be considered as well. I have articles and information on all types:

  7. Hi Dr. Childs,
    I was born hypothyroid with only a sliver of a thyroid gland. It produces some thyroid hormone but not consistently and I’ve been on synthetic all my life. I’ve been told there is no natural option and will always have to be synthetic. I am now reacting badly to Synthroid (was previously taking Levoxyl for years.) I have chronic hives covering my back, chest and neck, get so many headache, stomach issues, fibromyalgia worse than ever and just feel all around horrible. I mostly try to avoid gluten and dairy. My endocrinologist ignores my symptoms and only cares what the bloodwork says. Is there any natural supplement you know of that I could ask my Dr about that may be worth a try? Thank you so much.

  8. Hi!
    I used to take syntroid only between 2007 and 2021. I wasn’t feeling very good and the hypothyroidism symptoms were still obvious. Then I ask to switch to Erfa Thyroïd. The transformation was spectacular! Really, in few days I was feeling better and after few months I was feeling great! Then my blood test were showing hyperthyroidism. The doctor said NDT was hard to follow as the dose might be variable from batch to batch because is a natural product. So she gave me cytomel 5mcg and synthroid 0.1mg. I insisted to get synthroid 0.05mg X 2.
    I felt bad after about 36 hours. I was bloated, my stomach and abdomen hurt, my joint hurt, felt tired, start to be constipated, having gastric reflux, felt upset and of course got into an insomnia cycle. After 10 days, the doctor changed to Cytomel 10mcg and Synthroid 0.05mg. I got better, but all the symptoms remained but less severe.
    My question: is it possible to be allergic to Synthroid?
    That could explain the spectacular transformation when I switched to NDT.
    Thank you for your help 🙂

    • Hi Louise,

      It’s possible to react negatively to the inactive ingredients found in Synthroid, but not the thyroid hormone component. The same T4 (thyroxine) that is found in Synthroid is also found in NDT, but the inactive ingredients differ.


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