Informational Posts

Being Hypothyroid with a Normal TSH

Being Hypothyroid with a Normal TSH
Originally published on 13th May 2016
Last updated on 20th November 2019

Have you been told that your TSH is ‘normal’, ‘fine’, ‘OK’,  or ‘in range’, yet still have thyroid symptoms?

You may or may not be on thyroid medication and have a TSH as described above, and still be hypothyroid.

You could be hypothyroid at a cellular level, due to conversion problems of thyroid hormone T4 into T3.

The Difference in Thyroid Hormones 

The most prescribed thyroid medication is a T4-only synthetic, such as Levothyroxine and Synthroid. T4 is reported to be about 90% of what the thyroid gland produces, with around 9% being T3. Some of the hormone T4 also converts in to T3, or at least it should, and adequate levels of both are needed to help us feel well and carry out all our usual bodily functions and processes.

What is a Conversion Problem?

An inability to properly convert T4 to T3 is common among thyroid patients and can result in a fluctuating TSH or a TSH that is ‘in range’ and a low Free T3.

Many patients have an in-range TSH, but when they actually check their Free T3 and Free T4 levels, they see that the T4 in their T4-only medication is not converting into enough T3.

Conversion issues can be caused by an enzyme called iodothyronine deiodinase that is either deficient or not compatible for some people. The enzyme iodothyronine deiodinase is important in the activation and deactivation of thyroid hormones. T4 is converted into T3 by deiodinase activity.

Another possibility for conversion issues can be adrenal dysfunction or other vitamin deficiencies such as iron or seleniumPoor gut health can also be a contributor.

By addressing these, you may fix the conversion problem, but many other people simply have a problem converting T4 to T3 and don’t know why. But it’s a big reason as to why T3 and NDT medication can work better for a lot of patients, instead of T4-only medications like Levothyroxine or Synthroid, because it gives the patient direct T3, so they do not have to rely on their body to convert it.

Test Results 

The optimal TSH level of below 2.5 or 2 is well-reported, but many doctors are still using an out-dated reference range which allows TSH to up to 5 or even 10, and feel that anyone falling within this wide range is adequately managed, even giving the diagnosis of ‘borderline’ or ‘subclinical’ hypothyroidism.

However, if your hypothyroidism is not properly managed, it puts you at risk of developing other health conditions, whether thyroid hormone levels are too high or too low. So we should be aiming for an optimal TSH of below 2.5 or 2.

If your TSH is within the recommended optimal range and you still don’t feel well, you should ensure that your Free T3 and Free T4 also sit in the optimal places in range. Other key tests, like adrenal function, are explained here.

A Note on Reverse T3

Another factor to take in to consideration could be your Reverse T3 levels. Reverse T3 is an inactive form of T3 and is often said to create a thyroid problem at the cellular level, with a normal TSH level. Other thyroid test results can look normal, yet Reverse T3 remains an issue.

However, please see here as to why testing Reverse T3 is often controversial and why I’m dubious about whether it’s truly useful. I lean more towards ‘no’, however, you will see other thyroid resources suggesting we must have it checked.

Have you been told your test results are ‘normal’, yet still experience ongoing symptoms?

You can click on the hyperlinks in the above post to learn more and see references to information given.

Be Your Own Thyroid Advocate Book Cover

See also:

The book Be Your Own Thyroid Advocate: When You’re Sick and Tired of Being Sick and Tiredwhich builds on this article in detail.

About Author

Rachel Hill is the highly ranked and multi-award winning thyroid patient advocate, writer, speaker and author behind The Invisible Hypothyroidism. Her thyroid advocacy work includes writing articles, authoring books, producing her Thyroid Family email newsletters and speaking on podcasts and at events about the many aspects thyroid disease affects and how to overcome these. She is well-recognised as a crucial and influential contributor to the thyroid community and has a large social media presence. Her bestselling books include "Be Your Own Thyroid Advocate" and "You, Me and Hypothyroidism".


  • Sally
    November 15, 2022 at 8:22 pm

    Ms Hill, your research and knowledge is amazing . For years now ,my tsh has been up ,down , up down. It started at 4 then it would go to 1 , then last year it went from 3.6 to 0.02, and I’ve been on the same dose for years 100mcg, even when my tsh dropped so low. Its now 0.35 , fatigue,dry skin,hair coming out in clumps, no energy, double vision all the time,blurry, I won’t take the anti depressant the doctor gave me.
    My tsh is now 0.35 my ft3 is 5.6 and my ft4 I think it’s either 1.9 or 19 …. I don’t think it has a dot in between it. I just don’t know what to do. Doctors don’t listen. Why is my tsh swinging up and down all the time ?

  • Kristen Jones
    April 19, 2021 at 9:40 pm

    How do you test deficiency or non compatability in iodothyronine deiodinase ?
    I’m positive i do not convert well but my vitamin/mineral levels are good

  • Mary Henderson
    January 5, 2021 at 10:22 pm

    Ms. Hill; thank you for your contributions in assisting thyroid issues. I’ve just come across this site. I can’t find a doctor who can help and was told conversion issues are genetic and diagnosed when one is a baby. I can’t get my thyroid stable and my biggest complaint is the cognitive issues, brain fog, no motivation, and major fatigue. I’m currently on 100 mcg of T4 and 20 mcg of T3 compounded. TSH, T4, and free T3 are all low. This is secondary hypothyroid and they believe it is in connection the HPA system. What would be your best resource to review to find answers with this hypothyroid issue. I need to find possibly a new doctor as well. I’m at a loss. I went from biking 100 + miles a week to barely being able to muster the energy for work. I was fine for years on desiccated and then it started to fail after I was hit on my bike. I need help. It’s caused great depression. Thanks for any and all advice with where to start. Kindly, Mary


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