Healthy Hormones

Why is My T4 Low (and What Can I Do About It)?

Do your lab tests show that your T4 level is low?

What does that mean exactly?

Do you also have symptoms such as fatigue, weight gain, hair loss, constipation, and depression?

If you answered yes, you most likely have hypothyroidism which usually causes a low T4 level.

In this article, I will discuss the T4 lab test, what it means when it is low, symptoms that may be associated with a low T4 level, and I will also give some treatment tips that will help raise it to an optimal level.

Let's get started...


What is T4?

So what is T4 anyway? 

In order to answer that question, we need to talk about the thyroid gland and how it works.

The thyroid gland primarily produces 2 types of thyroid hormone - Thyroxine (T4) and Triiodothyronine (T3).

The vast majority of the thyroid hormone produced is thyroxine (T4).  Not nearly as much triiodothyronine (T3) is produced.

Both of these hormones are produced in response to a hormone secreted by the pituitary gland called Thyroid Stimulating Hormone (TSH).

The association of TSH and T4 gives us valuable information about how well the thyroid gland is working. That is why these tests should always be tested together.

So what is the purpose of T4 in the body?

T4 is not nearly as biologically active as T3, but it still helps regulate how much T3 is available in the body.  

Most of the T3 in the body is actually produced from peripheral conversion of T4.  

More specifically, as the body needs T3, an enzyme called a deiodinase will cleave off an iodine molecule from T4 which converts it into T3.

You can therefore think of T4 as a storage reservoir for the body to use to make T3 as it needs it.  This is the primary purpose of T4.

Causes of Low T4

So what happens if the T4 level is low?

If the reservoir of T4 becomes low in the body (sort of like most of the lakes in the Texas Panhandle where I live), then there is not enough substrate that the body can use to produce T3.

The T3 levels then also drop, and symptoms of hypothyroidism develop.

Why does the T4 level drop?

Let's discuss the most common causes:

1.  Autoimmune Thyroiditis (Hashimoto's) -

There are many theories about how and why autoimmune disorders develop.

It is generally accepted that 3 things must be in place for an autoimmune disorder to develop.

  • Genetic Predisposition - You have a variation in one of your genes that may make it more likely to develop an autoimmune condition.
  • Leaky Gut - The bacterial levels and types of bacteria in your GI tract may be inadequate.  Also, gaps between the cells in your intestines may widen which allows foreign proteins and toxins to enter the bloodstream that wouldn't normally get through.
  • Trigger - A physical or emotional event may occur (injury, surgery, major life stress, etc.), or you may be exposed to an environmental toxic of some sort which can damage your immune system and cause it to function improperly.

A common theory is that some of these foreign proteins that enter our bloodstream look similar to proteins in our body.  As a result, as our immune system makes antibodies against these foreign proteins, it in effect also unintentionally makes antibodies against parts of our body.

This is called molecular mimicry.

This appears to be what happens in Hashimoto's Thyroiditis.

The result is these auto-antibodies continuously attack parts of our thyroid gland, gradually destroying it.

As the cells of the thyroid gland are destroyed, its ability to produce thyroid hormone is impaired and hypothyroidism will develop.

This typically occurs slowly over many years.

Often patients will have classic symptoms of hypothyroidism, but their labs will remain relatively normal until late in the process.

Hashimoto's is an extremely common condition.  In fact, in my medical practice I typically diagnose one or more people with it every week!  It is by far the most common autoimmune disorder.

Many experts believe that the vast majority (over 90%) of hypothyroidism in the United States is actually caused by Hashimoto's.

If you have hypothyroidism, you should periodically have your thyroid antibody levels checked.

Click here to read more.

2.  Hypothyroidism -

Hypothyroidism refers to the condition of low levels of thyroid hormone in the body.

The majority of cases are due to issues with the thyroid gland itself.  Rarely, it can be caused by issues in the brain (hypothalamic dysfunction).

Since most thyroid hormone in the body is T4, if you are hypothyroid, you will have low levels of T4.

That, however, does not give you enough information.  You need to investigate WHY you have hypothyroidism so that you can be appropriately treated.

As we discussed earlier, the majority of hypothyroidism is caused by Hashimoto's Thyroiditis.

3.  Nutrient Deficiencies -

There are multiple (at least 13) nutrients that are needed for proper thyroid hormone production and conversion.

A deficiency of even one of them can result in a significant reduction in thyroid levels which will cause symptoms of hypothyroidism.  It can also cause an increase in thyroid antibody levels if you have Hashimoto's.

These nutrient deficiencies can include (click on the names for my preferred brands):

So, should you just blindly supplement with all or most of these supplements if you have thyroid issues?

Of course not!

You should always see your doctor and be tested for any nutrient deficiencies before supplementing, or at least look for common symptoms associated with particular deficiencies.  If you have a symptom or symptoms commonly seen with one of these nutrient deficiencies, then a trial of supplementation is reasonable to consider.

It is also always best to start with your diet.  Eat a diet high in nutrient-dense, organic foods which will contain a much higher nutrient content than the Standard American Diet.

4.  Taking a T3 Only Medication -

If you are taking a T3 only medication, it will often result in a drop in your T4 level.

T3 only medications include Cytomel and liothyroinine.  

Why?  It makes sense if you think about it.

Like we learned earlier, T4 acts as the storage reservoir for T3 in the body.

If you are taking a T3 only medication, then your need for that reserve of T4 decreases because you have bypassed the conversion process.  This therefore results in less T4 production by the thyroid gland.

Taking a T3 only medication will typically cause the free T4 level to decrease, the TSH level to decrease, the reverse T3 level to decrease, and the total T3 and free T3 levels to increase.

This can also happen to a lesser extent if you are taking a natural dessicated thyroid (NDT) such as Armour Thyroid, NP Thyroid, or Nature-throid.  That is because these medications contain about 20% T3 and about 80% T4.

The drop in T4 level in this case is expected and what you want.  It is not a sign of inadequate thyroid levels like it is in the other situations.

Symptoms of Low T4

Having a low T4 level typically results in all of the classic symptoms of hypothyroidism.  

The list of symptoms can be quite exhaustive, but the most common include:

  • Fatigue
  • Weight Gain
  • Hair Loss
  • Constipation
  • Cold Intolerance
  • Depression
  • Brittle Nails
  • Dry Skin
  • Menstrual Irregularities
  • Infertility
  • Brain Fog

For a more extensive list, click here.

The vast majority of doctors have been taught to use the TSH as their sole means of evaluating thyroid function.

In many cases of hypothyroidism, the TSH will remain normal until it has been present for many years. This is true with Hashimoto's as well.

The T4 and T3 levels will typically drop earlier in the process than will the TSH.

That is another reason why you should ALWAYS ask for a complete thyroid panel when your thyroid is being evaluated.

How to Raise Your T4

Fortunately, raising your T4 level is usually straight-forward.

Reversing what is causing your low T4 is the key to successful treatment.

You will either want to increase the thyroid hormone your body produces itself, or you will need to supplement what your body produces with a thyroid hormone medication.

1.  Lifestyle Interventions -

Improving your diet, beginning an exercise program, improving gut function, and reducing stress should always be the first steps taken when treating ANY condition.  The thyroid is no exception.

2.  Correct Any Nutrient Deficiencies -

Identifying and correcting any of the nutrient deficiencies we discussed earlier will result in an increase in your body's natural thyroid production and T4 to T3 conversion.

3.  Supplement with a T4 Thyroid Hormone - 

Taking a T4 only medication such as levothyroxine, Synthroid, or Tyrosint will result in an increase in the T4 level in the body.  

Keep in mind that if you have T4 to T3 conversion issues because of a nutrient deficiency or inflammation in the body (insulin resistance, leptin resistance, an autoimmune condition, etc), raising your T4 level may still not result in adequate T3 levels reaching the cells.  Symptoms of hypothyroidism may still not improve.

4.  Reduce Thyroid Antibody Levels -

If you have Hashimoto's, there are dietary, supplement, and medication therapies that can help reduce thyroid antibody levels.  This will improve thyroid function and will help to raise the T4 to an optimal level.

Click here to read more.

5.  Take T3 Thyroid Hormone -

In addition to or even in place of T4 thyroid hormone, T3 hormone medication can be taken.

That may cause the T4 level to drop, but that is not a bad thing in this case.

There is an art to using T3 medication, so it is important that you find a medical provider with experience in using it.

Click here to read more.


A low T4 level is commonly seen in hypothyroidism.  It is often present before the TSH level becomes abnormal.

A low T4 is associated with several symptoms that can dramatically alter your quality of life.

Treatment to increase T4 levels typically involves correcting nutritient deficiencies, reducing inflammation, and taking thyroid medication.

Now it's your turn...

Is your T4 level low?

Is your TSH level low, normal, or high?

Are you having symptoms of hypothyroidism?

What treatment plan are you using?

Leave any questions or comments below.

About the Author Dr. Jeff Whelchel

Dr. Whelchel is a family physician who specializes in functional medicine, especially hormone optimization. He has over 20 years experience in private practice managing patients with various medical issues. His passion is helping patients reach their full potential of wellness and quality of life. He grew up in the Texas Panhandle where he currently lives. He is married and has 3 awesome children.

Leave a Comment:

Janice Dawson says June 27, 2018

Please add me to your comments when posting new thyroid updates.I had my thyroid taken out because of cold nodule

    Dr. Jeff Whelchel says June 27, 2018

    Hi Janice. If you will click on an article on my website, a popup window should appear asking if you want to join my newsletter for free. If you will sign up there you will get an email every time a release a new article. Take care.

Kimberly K Butler says August 21, 2018

On levothyroxine…levels better but symptoms continue. Have all symptoms. Advice? Doctor only checks TSH and T4.

    Dr. Jeff Whelchel says August 21, 2018

    My advice is to ask your doctor to also check a free T3, reverse T3, TPO antibodies, and thyroglobulin antibodies. If they won’t, then find a different doctor. Your thyroid hasn’t been fully assessed yet.

Amanda S says March 4, 2021

You have simplified the answers I have been looking for. Thank you so much much for this!!

Amanda says March 31, 2021

Diagnosed Hashimoto for 12 years. 42 years old. My tsh is 1.68, free t4 0.7, ft3 2.73, total t3 108. I am on np thyroid and lots of vitamins. My hair is thinning I feel anxious and have some insomnia. I stopped the selenium and iron for a bit bc I was on the high end but thjnking I should add back in. I also take a low dose of algazim (kelp iodine). My question is where should my free t4 be. Are my symptoms bc of the low free t4?

    Dr. Jeff Whelchel says April 11, 2021

    I think your issues are more low t3 which I like >3.5. You need to sit down with your doctor about it. I hope you feel better soon.

Michele Blum says April 28, 2021

i have just been informed that my T4, free is 0.78 results low….what does this mean?

    Dr. Jeff Whelchel says May 30, 2021

    It is impossible for me to interpret just a single lab result. I would need to see the complete thyroid panel plus get a history of symptoms and other medical issues.

Christine C says July 13, 2021

Thankyou for your thoughtful discussion of the delicate balance – I am using NP thyroid and now my all my levels are low TSH as well so my symp are hypo. And I’ve been treated for hypo but now my TSH seems to indicate Hyper!
I need to find a good specialist to get on track and am not sure if I should just stop the NP thyroid until I do get to doctor -as it hasn’t been effective and it has been 6 months. I am at 90 mg . Do you think I should stop it I’ve now heard verybad reports 0f that particular drug.

    Dr. Jeff Whelchel says July 17, 2021

    Hi Christine. I would NOT stop the NP thyroid. In my experience, your TSH may have to be suppressed in order to get your free T3 and free T4 levels in the optimal range. Please follow up with you doctor and communicate any symptoms or side effects that you are having.

Sophie says July 22, 2021

Dear Dr Whelchel, I understand what you said about T4 not being relevant if you are on T3, but I have not found this to be the case. i am hypopituitary and my T4 went down to 1 (the lowest in the Uk range is 12) and I have been very unwell for several years, thinking that my T4 did not matter. A new endicronologist said that this was not true and I was in real danger. I have now added T4 (as well as T3) and been working for months to bring myself into range (still not there) and still suffer extreme fatigue. I would be interested to know your thoughts. Kindest, Sophie

    Dr. Jeff Whelchel says July 25, 2021

    Hi Sophie. I did not mean that T4 is irrelevant. My intent was to say that I am not concerned if the T4 level drops a bit when someone it taking a T3 medication. Everyone is unique and different. If keeping your T4 level higher helps you, then great! I’m glad you found something that helps.

Galaxy says August 3, 2021

Hi my T4 levels are in 2013 8.9, in 2014 10.1, and in 2019 11.2, do you think this is low? my doctors are dismissive as the other level is normal, but i do have a few of the symptoms suggested and my mother was also given thyroid medication in her 60ies. I am 66.

    Dr. Jeff Whelchel says August 7, 2021

    Hello. It’s really impossible for me to answer that without knowing more of your history and seeing all of the lab results.

Puzzled says September 13, 2021

DR Jeff: Excellent article and really helped my understand the likely treatment path for my high TSH/low T-4 levels!

    Dr. Jeff Whelchel says December 22, 2021

    Thank you for the compliment. I’m glad it helped you.

chezron says December 25, 2021

Really enjoyed this article on thyroid levels. You explained it very well.

Karen says March 8, 2022

Is Armour Thyroid a T-3 only medication? I do not have Hashimoto’s and Synthroid and levothyroxine have not resolved issue of low T4. Switched to Armour Thyroid, but still low T4, so your helpful article caused me to wonder if it is a T3 only medication. Thank You for this helpful article.

    Dr. Jeff Whelchel says May 10, 2022

    Armour Thyroid is about 80% T4 and 20% T3. You likely need to increase the dose of your thyroid medication, even if it makes your TSH become suppressed.

crystal dunbar says March 26, 2022

my free t4 is 0.7 and my tsh 1.92 what should i be eating to get my free t4 up to normal

    Dr. Jeff Whelchel says May 10, 2022

    Diet alone may not be enough to raise your free T4 level. I would also recommend that you get a complete thyroid panel drawn – TSH, free T4, free T3, reverse T3, TPO antibodies, and thyroglobulin antibodies. The 2 lab results just don’t give enough information to know what is going on with your thyroid.

renee schulz says March 30, 2022

Hi Dr Whelchel, My free t4 is .6, tsh .010, thyriod perixdase antibody 198, free t3 is 3.8. I am on 25mcg of lio, 75mcg of levo both one per day. I am still flaring and get horrible facial swelling. What are your thoughts?

    Dr. Jeff Whelchel says May 10, 2022

    Sorry you are still flaring. Your lab results aren’t surprising in light of your Hashimoto’s and taking T3. I would be focusing on lifestyle issues – gluten-free, dairy-free, good sleep hygiene, stress management, etc. All of that should help.

Shibin Raveendran says July 13, 2022

I’m 35, and I had diagnosed with hypothyroidism five years. Though, the TSH level was 149. I had no symptoms of hypothyroidism. I repeated the test in different laboratories, but the result was the same.
My doctor advised me to take thyroxin (100Mg) for three months, and I started medication based on that. Then the doctor advised me to check my TSH after one week. Surprisingly the TSH level dropped to 4.0. ( FreeT3 and T4 were also in the normal range). The doctor then advised me to stop the medication.
Two days back, I again had a check-up. In the report, my TSH level was 93.97. But, still, I do not have any symptoms. Also, I have a deficiency of sodium and VitaminB12.

Below is my test report,

Thyroid Stimulating Hormone (TSH) 93.97ulU/mL (Ref range:0.450 – 5.330)
Tri-iodothyronine – Total (TT3) 1.67nmol/L (Ref range:1.34 – 2.73)
Thyroxine- Total (TT4) 54.69nmol/L (Ref range:78.38 – 157.40)
Testosterone – Total 3.62ng/mL (Ref range:1.75 – 7.81)

I seek your advice.

    Dr. Jeff Whelchel says July 25, 2022

    Hello. I would need several other lab results before I could accurately assess your situation. I would need to know the free T4, free T3, reverse T3, TPO antibodies and thyroglobulin antibodies. Based on just the TSH alone you are hypothyroid, but more workup is needed.

      Shibin Raveendran says July 26, 2022

      Thank you, Dr Jeff.
      I will be back with the suggested test reports.

      Shibin Raveendran says July 31, 2022

      The requested lab reports are ;

      Tri-iodothyronine – Free (FT3) 5.38 pmol/L(Ref3.80 – 6.00)

      Thyroxine – Free (FT4) 5.00 pmol/L(Ref 7.86- 14.41)

      Thyroid Stimulating Hormone (TSH) 78.480 ulU/mL(Ref 0.450- 5.330)

      Thyroglobulin Ab (Anti-Tg) >2500 (Ref10000 (Ref<9)

      The result, after appropriate dilution, is above the Clinically Reportable Range(CRR) of the assay. The upper limit of detection which is
      10000 IU/mL have been Reported

        Dr. Jeff Whelchel says January 5, 2023

        Your labs look like severe Hashimoto’s thyroiditis with secondary hypothyroidism. You need to see someone near you that is a thyroid specialist.

Angie says July 20, 2022

I have hashimotos I take 75 mcg Tirosint and 40 mcg liothyronine .. my labs showed my free T 4 is below range . .. Do I increase the Tirosint ..? Thank you

    Dr. Jeff Whelchel says July 25, 2022

    That all depends on what the other labs show. Liothyronine tends to suppress T4 levels, so it may not be needed. However, in order to answer your question, I would need to know the TSH, free T3, and reverse T3 levels.

Edward Allen Morzak says August 8, 2022

thx, very informative in layman’s terms.

    Dr. Jeff Whelchel says January 5, 2023

    Thank you for the compliment.

Tristain says October 1, 2022

Is it normal for my FT4 to drop after starting Tirosint? I was at .82 and 6 weeks in it had dropped to .79. My FT3 did rise from 2.36 to 2.76 though. It just seems strange thistle I’m taking T4 meds and yet mt T4 is dropping. Some symptoms are still there, others seem to be a little better.

    Dr. Jeff Whelchel says January 5, 2023

    I would suspect that the slight drop in your FT4 is likely due to lab variance. If anything, taking T4 medication should raise your FT4.

Steven H says October 30, 2022

My first results were high TSH and low FreeT-4, I had never been tested for this before, so before starting medication I requested a retest, My Dr. agreed, re-tested and free T-4 , .064, and TSH 10.3072, but I see nothing for T-3, reverse T-3, TPO, and thyroglobulin anti-bodies. Are these necessary for treatment?

    Dr. Jeff Whelchel says January 5, 2023

    Those results definitely fall in the hypothyroid range. I would insist on getting the other lab tests before starting any treatment, however. They will influence what your best treatment would be.

Jill A Farley says November 25, 2022

My tsh 8.600 , free T4 0.47, free T3 3.3 take np thyroid 60 because others side effects cant T the right level. Called Dr. today waiting for answer iam 83 , since fall 99 is 60 too high of mg or what

    Dr. Jeff Whelchel says January 5, 2023

    60mg is a very common dose. I have some patients that have to take 180mg or more. Just be careful at your age and notify your doctor if you develop any symptoms of hyperthyroidism – palpitations, shakiness, tremor, etc.

Andrea Montes says January 2, 2023

Hi Dr Whelchel , this are my recent labs, my t4 levels go up and down all the time and my Pcp doctor don’t see the necessity to treat it, so I went to an endocrinologist, and we will see what happen.
I would like to know your opinion though, thank you.
Trans. Growth Fact. beta 1* 01 7525 High, T4,Free(Direct) 02 0.77 Low, TSH02 3.470 ,Complement C4a03 1063.0 High, Reverse T3, Serum A, 03 10.6,MTHFR, DNA Analysis 04
c.665C>T (p. Ala222Val), legacy name: C677T – Detected, Thyroid Peroxidase (TPO) Ab02 <9 ,Thyroglobulin Antibody 02 <1.0 ,Triiodothyronine (T3), Free 02 2.3

    Dr. Jeff Whelchel says January 5, 2023

    Hi Andrea,
    Those results would definitely fall into the hypothyroid range. If your doctor won’t offer a treatment, you may need to seek another medical provider.

Nancy Blotter-Northway says February 10, 2023

Very informative easy to understand. Thank you!!!

Pat Gregoire says April 11, 2023

I am on levothyroxin and Liothyronine. My new primary care physician reduced my levoththyroxin after lab results showed my T4 was “suppressed”. He said it would help my fatigue. My impression from this article is that information may not be correct. Am I interpreting it correctly?

Angie says May 23, 2023

Do you do phone consultations? No one can seem to get my hypothyroidism under control.

Alena says May 27, 2023

I have hashimotos, my TPO antibodies are well above 900 (labs max). I take NP thyroid 60mg daily. My question is would NP thyroid cause further increase in TPO antibodies? Since it’s similar to thyroid tissue. Wondering if going to levothyroxine would help reduce TPO for me. Thank you.

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