What Your Low TSH Means While taking Thyroid Medication & Why it isn’t Helpful
Would it surprise you to know that you can have a LOW TSH but still be hypothyroid?
This situation is not uncommon and may be occurring in your body right now.
Your TSH can be a helpful tool in evaluating thyroid function in the body but it certainly isn't the only tool (and it isn't even the best).
Learn how to evaluate your TSH and what a low TSH means if you are taking thyroid medication in this post:
What does your TSH actually mean?
When we talk about your TSH we need to make some qualifications.
Your TSH (thyroid stimulating hormone) is a hormone secreted from your pituitary gland.
It's supposed to target your thyroid gland directly which results in the production of thyroid hormone from the gland.
Basically it does exactly as its name suggests: stimulates thyroid hormone from the thyroid gland.
So why is this important?
The current paradigm of thyroid treatment and replaces puts a considerable amount of weight on this ONE test.
Your thyroid status in your entire body is evaluated based on this serum marker.
We will talk about why that isn't necessarily a good thing in a moment, but we need to stay on track.
So how does your TSH level alter your thyroid hormone?
Assuming that you are NOT taking thyroid medication (this assumption is very important) a high TSH (generally) would indicate that you are not producing enough thyroid hormone.
Now this can be confusing for some people...
How can a HIGH TSH mean that I have low thyroid hormone if TSH is supposed to make my thyroid gland produce more thyroid?
Great question and here's where things get interesting.
Just because your TSH is HIGH doesn't mean that your thyroid gland is able to produce thyroid hormone.
Because producing thyroid hormone requires at least 13 different nutrients including iodine, B vitamins, vitamin A, etc. (You can see the full list here).
So if your body CAN'T produce the thyroid hormone even though your brain is screaming at it to do so then your TSH will rise but your thyroid hormone will fall.
This same process can (and does) occur in conditions like Hashimoto's thyroiditis.
If your thyroid is unable to produce thyroid hormone because it has been damaged from autoimmune disease then your TSH will rise over time as well.
So what about a low TSH?
A low TSH, assuming you aren't taking medication, is a sign that you may be hyperthyroid.
But that's not what I want to focus on here.
Instead I want to spend time explaining what happens to your TSH when you are taking thyroid hormone.
Most providers would have you believe that a low TSH in the presence of taking thyroid medication is a sign of hyperthyroidism.
This would indicate that you need to LOWER your dose of thyroid medication to achieve a euthyroid status in the body.
But is this true?
Does a low TSH while taking thyroid medication actually mean that you are hyperthyroid?
If that is the case then why do patients taking thyroid medication for symptoms of hypothyroidism STILL have symptoms of hypothyroidism as their TSH drops? Even to low levels?
What Happens to your TSH when taking Thyroid Hormone:
It turns out that the TSH is a really good predictor of what is happening in the pituitary gland itself, but it doesn't necessarily tell you how much thyroid hormone is getting into your other tissues.
And this is important because almost every cell in your body has a thyroid receptor.
So the TSH would be a great predictor of thyroid function in the body IF your pituitary gland was just like every other tissue in the body, but it isn't.
Your pituitary gland has special deiodinases which are different than other tissues in the body making it MORE sensitive to thyroid hormone than other tissues.
What does this mean?
It means that as you give someone thyroid hormone (especially T4) their pituitary gland will sense the thyroid hormone and drop the TSH in accordance.
But your other tissues may NOT get the thyroid hormone.
This results in patients who have a normal or low TSH but still have symptoms of hypothyroidism.
Do all thyroid hormones alter the TSH equally?
And in order to understand this we need to talk about basic thyroid physiology first.
The two most important thyroid hormones in circulation include T4 and T3.
T4 is the inactive thyroid hormone in your body, but it has POTENTIAL to be activated by deiodinases after cleaving off an iodine moiety turning it into T3.
T3 is the ACTIVE thyroid hormone in your body. It turns on genetic transcription resulting in changes to your genes and the production of enzymes in your cells.
Why is this important?
Because most thyroid hormone that is used as replacement is in the T4 form.
Meaning the thyroid hormone that doctors give you MUST be activated before your body can actually use it.
But here's where things get interesting:
Your pituitary gland has no problem activating T4 into T3, in fact it does this quite well.
But other tissues in your body have to compete with an inactive thyroid metabolite known as reverse T3.
Reverse T3 is the ugly stepsister of T3 and directly competes with T3 for binding and turning on genes.
Oh, and reverse T3 is created from T4 just like T3 can be.
So this means in most tissues in your body there is a tug-of-war going on between T3 binding and reverse T3 binding.
But this tug-of-war is NOT happening in your pituitary gland.
This is why basing your dosing decisions off of the TSH by itself is not necessarily a wise decision.
So how does taking thyroid hormone alter your TSH?
Taking either T4 or T3 will reduce your TSH, no question about it.
It turns out that T3 is about 3-4x more powerful at reducing your TSH than T4 is but they will both reduce it.
So if your TSH isn't the best way to evaluate thyroid function.... what is?
Using Free T3, Free T4 and Reverse T3 for the Whole Picture
If you want to get a picture of what is actually happening in your thyroid gland then you really need to order more than just the basic TSH.
Ordering the FREE thyroid hormones (like Free T3, free T4 and reverse T3) can help give you an idea of what kind of competition exists for binding in your body.
We know that T3 is the "good" thyroid hormone, so we can conclude (under normal circumstances) we probably want more free T3 in our body than reverse T3.
Because if they are both competing for binding on your cells, we probably want the good guy to win.
So it makes sense that if we test your thyroid hormone and you have LOW free T3 with HIGH reverse T3 levels that probably isn't a good thing.
This condition is known as thyroid resistance.
But what is the TSH doing in situations like this?
Your TSH may be normal in this type of condition making diagnosis difficult.
Because really what is happening is that you have a tissue level hypothyroidism with "normal" blood levels of thyroid hormone.
Now your next question should be: is this common?
And the answer is that yes, it is more common than you think.
If you want to get an idea of what is actually happening in your body you need more than just the TSH.
I recommend this complete thyroid panel:
- TSH (Yes it is still helpful to have)
- Free T3
- Free T4
- Reverse T3
- Total T3
- Thyroid antibodies
- Bottom line: You need more than just your TSH to determine what is actually happening in your body. Make sure that you get a complete thyroid panel when evaluating your thyroid function.
What is a Normal TSH?
Even though we know that the TSH isn't necessarily the best test to use to diagnose or manage hypothyroidism it still has some value.
So what is the ideal TSH level?
Well, that depends on whether you are on thyroid medication or not.
Ideal TSH levels based on your condition:
- Not taking any thyroid medication - Generally healthy populations (not on thyroid hormone) have a TSH less than 1.0
- On Thyroid medication - Your TSH may fluctuate dramatically based on whether you are taking T3 or T4, but in most cases you will want a TSH that is less than 1.0 (mimicking the "healthy" state described above)
What's interesting is that the reference range for the TSH ranges from 0.300 to 5.00 in most cases.
But this represents the REFERENCE range, not necessarily the OPTIMAL range.
Focus on the optimal range I've listed above if you want to feel normal and you can read more about optimal ranges in this post.
What does it mean if your TSH is low and you AREN'T taking thyroid medication?
If you are NOT taking thyroid medication and you have a low TSH then that truly might be a sign that you are hyperthyroid or have a condition known as subclinical hyperthyroidism.
But this same concept doesn't necessarily hold true if you are taking thyroid hormone (although it may).
So let's talk about what can happen to your thyroid while on thyroid medication:
Low TSH but Normal T4 & T3
If you are taking thyroid medication is it possible to have a LOW TSH but normal T4 and T3?
Yes, you can definitely have a low TSH with normal free thyroid hormones.
But what does this actually mean?
If you fall into this category then you will need to use more than testing to determine what is happening in your body.
If your TSH is low and your free T4/T3 levels are normal but your body temp is low, your resting heart rate is low and you have all the symptoms of hypothyroidism - are you really "normal"?
The answer is obviously not, and that's why you need more advanced measurements to determine what is happening in your body.
If, on the other hand, your TSH is low and your free T3/T4 levels are normal but you are having symptoms like heart palpitations or anxiety then it may simply be that your dose is TOO high.
Yes, both conditions can and do happen which is why constant adjustments of thyroid dosing is necessary.
Some people are exquisitely sensitive to thyroid hormone (including even T4 thyroid doses) which can create strange symptoms that may include both a mix of hyperthyroidism and hypothyroidism.
In these cases it's best to determine if your symptoms coincide with changing your medication and if other factors (such as body temp, heart rate, etc.) imply your thyroid hormone is too high/low.
- Bottom line: A low TSH with normal T3 and T4 levels may indicate subclinical hyperthyroidism if you are not taking thyroid medication, or a hypothyroid state if you are taking thyroid medication.
Low TSH with symptoms of Hypothyroidism
Is it possible to have a low TSH but still have symptoms of hypothyroidism?
As I've mentioned previously your TSH only tells you how much thyroid hormone is influencing your pituitary.
It does NOT tell you how much thyroid hormone is influencing your hair follicles, cardiac tissue, skeletal muscles, insulin receptors etc.
If you don't have enough thyroid hormone hitting your hair follicles you will have hair loss.
If thyroid hormone doesn't hit your heart cells then your heart rate will slow and so will your metabolism.
If it doesn't get into your skeletal muscles then you may present with chronic pain and muscular pain.
If it doesn't come into contact with your insulin receptors then you may develop insulin resistance.
The list goes on and on.
If you fall into this category then you may simply need more thyroid hormone or you may ultimately need to switch to a different type of thyroid hormone that contains T3.
- Bottom line: You can have a low TSH with symptoms of hypothyroidism. This occurs when your cells are not getting enough thyroid hormone but your pituitary is.
Low TSH and Weight Gain
Is it possible to gain weight with a low TSH?
The answer is ABSOLUTELY.
In fact this happens all the time.
If thyroid hormone actually made people lose weight don't you think there would be weight loss clinics pushing thyroid hormone like crazy?
Of course they would, and the drug companies would be fumbling over themselves trying to patent a new thyroid medication that they could make money from.
You don't see this happening because thyroid hormone (as a medication) is not a weight loss drug... necessarily.
In most cases, people who are gaining weight with a low TSH usually have 1 of 2 problems (or both):
- Conversion problems
- Allergies or sensitivities to the inactive ingredients of thyroid hormone
The conversion problem refers to having issues turning T4 into the active thyroid hormone T3.
If your body isn't good at converting thyroid hormone (from inflammation, infection, medical issues, etc.) then you will have plenty of T4 floating around in your system but very little T3.
The T4 floating around in your system can and will drop your TSH, but it doesn't mean that it's necessarily active in your cells.
You can test for this by looking at your free T3/free T4 levels and by evaluating your reverse T3 levels.
- Bottom line: High levels of reverse T3 can cause your TSH to drop and cause your metabolism to slow resulting in weight gain. To treat this condition you may need T3 containing medication.
Back to you...
Remember that while the TSH can be helpful, it isn't the only (or necessarily the best) way to determine what is happening with your thyroid.
Using a more comprehensive thyroid testing profile in conjunction with your subjective symptoms can help nail down what is actually happening to your body.
When talking about thyroid function it's important to remember how critical the conversion of T4 to T3 is in regards to how you are feeling.
High levels of reverse T3 with low levels of free T3 may indicate thyroid resistance.
In cases such as these your TSH becomes less helpful and can even be low.
Now it's your turn:
Do you have a low TSH but symptoms of hypothyroidism?
What about your free t3 and free t4 levels?
What TSH level do you feel "best" at?
Leave your comments below!