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Stressed Woman

You are taking any form of levothyroxine -- Levoxyl®, Synthroid®, Tirosint®, Tirosint®-SOL, Unithroid®, or generic levothyroxine -- and you still don't feel well.


Your thyroid levels are not at optimal levels.


One of the most basic challenges to effective hypothyroidism treatment is when your medication doesn’t appear to be helping you achieve optimal levels of thyroid hormone.

What does “optimal” mean? Let’s take a look. For thyroid hormones, there’s what’s known as the “normal range,” or reference range. This is the broad range that’s used to evaluate your test results. Some practitioners feel that all your thyroid medication needs to do is to get your levels “in the normal range” For those practitioners, where you are in the range is considered irrelevant.


But other practitioners – and many patients – know that even small changes in thyroid levels – within the normal range -- can mean the difference between feeling great, and having a long list of unresolved symptoms. So the goal is to get levels to what they refer to as the “optimal range,” defined as the range where the majority of patients feel best.


Here’s a quick review of the “normal” reference ranges for Thyroid Stimulating Hormone (TSH), Free Thyroxine (Free T4) and Free Triiodothyronine (Free T3), and what some physicians and patients have identified as the “optimal” ranges for those tests.

Thyroid Stimulating Hormone (TSH): For TSH – a pituitary messenger hormone used to evaluate thyroid function -- the reference range varies slightly from lab to lab. A typical reference range is .4 to 5.5 mU/mL. Levels below the range are evidence of hyperthyroidism, and levels above the range are considered evidence of hypothyroidism.

tsh test.jpg

Free Thyroxine (Free T4): Thyroxine – T4 – is an actual thyroid hormone, and Free T4 measures the circulating thyroxine available to convert into T3 (the active thyroid hormone.) The normal reference range for Free T4 is .4 to 1.8 ng/dl. Levels below the range are considered evidence of hypothyroidism, and above the range suggests hyperthyroidism.  The optimal range has been identified as the upper half of the range, or in this case, from 1.2 to 1.8. 

free t4 test.jpg

Free Triiodothyronine (Free T3): T3 is the active thyroid hormone. A small amount is produced by a working gland itself, and the remainder is produced as the body converts T4 into the active T3. Free T3 measures the available amount of circulating T3.

Free T3 can be confusing, because labs use three different types of measurement to report on results. That means there are three different reference ranges.


  • The normal reference range for Free T3 measured in pg/dL is 260 - 480 pg/dL

  • The normal reference range for Free T3 measured in pmol/L is 4 - 7.4 pmol/L

  • The normal reference range for Free T3 measured in pg/ML is 2.3 – 4.2 pg/ML

Levels below the range are considered evidence of hypothyroidism, and above the range suggests hyperthyroidism.  

The optimal range has been identified as the upper half of the range. Note however that many patients who take a form of T3 as part of their treatment – as well as the prescribing practitioners – report that levels at around the 75th percentile of the range is their optimization target.

free t3 test.jpg

So, as a starting point, work with your health care practitioner to safely adjust your levothyroxine dosage to find out whether "normal" levels are not enough, and learn where your optimal levels are for wellness and the best symptom relief. 


The Levothyroxine Deep Dive program is copyright © 2020, Mary Shomon. All rights reserved.

Levoxyl®, Synthroid®, Tirosint®, Tirosint-SOL®, and Unithroid® are registered trademarks. Product images and logos used with permission. 


Mary Shomon does not provide medical advice, diagnosis or treatment.


The contents of this video and material contained on the website ("content") are for informational purposes only. The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have learned from this video or site.

If you think you may have a medical emergency, call your doctor or 911 immediately. Mary Shomon does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned. Reliance on any information provided by Mary Shomon is solely at your own risk.

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