If you've been on levothyroxine for years and still feel exhausted, moody, foggy, heavy, and not quite yourself, you've probably been told your labs look fine. Your TSH is normal. Your medication dose hasn't changed. And the implication, spoken or not, is that the thyroid is being managed and something else must be causing how you feel.
That conclusion is frequently wrong, and it leaves a significant number of people undertreated for years while their actual thyroid function remains suboptimal. Being on thyroid medication and having a normal TSH is not the same thing as having an optimized thyroid.
The Problem with TSH as the Only Marker
TSH, thyroid stimulating hormone, reflects what the pituitary gland is signaling. When TSH is in the normal range, it means the pituitary is satisfied with whatever thyroid hormone is circulating. What it doesn't tell you is whether that circulating hormone is being converted into a form your cells can actually use.
Levothyroxine contains only T4, the inactive storage form of thyroid hormone. For your body to use it, T4 must be converted to T3, the active form that drives metabolism, mood, energy, cognitive function, temperature regulation, and dozens of other processes. That conversion happens primarily in the liver, gut, and peripheral tissues. It requires adequate selenium, zinc, iron, and other cofactors. It can be impaired by stress, inflammation, insulin resistance, gut dysfunction, and advancing age.
A normal TSH tells you the pituitary is satisfied. It doesn't tell you whether your cells are actually getting the active thyroid hormone they need to function.
When T4-to-T3 conversion is impaired, a patient on levothyroxine can have a perfectly normal TSH and still be functionally hypothyroid at the tissue level. The medication is being taken. The pituitary is content. The patient still feels terrible. This is not in their head.
Who Has Trouble Converting T4 to T3
Poor conversion is more common than most patients are told, and it affects certain populations disproportionately:
- Women over 40, where hormonal changes affect the conversion pathway and receptor sensitivity
- Perimenopausal and menopausal women, where declining estrogen compounds thyroid dysfunction in ways that standard panels don't capture
- People with chronic stress and elevated cortisol, which drives T4 conversion toward reverse T3 rather than active T3
- Patients with insulin resistance or metabolic dysfunction, where impaired glucose metabolism affects thyroid hormone utilization
- Anyone with gut or liver dysfunction, since these are primary sites of T4-to-T3 conversion
- People with nutrient insufficiencies in selenium, zinc, or iron, which are required cofactors in the conversion process
What a Complete Thyroid Panel Should Include
If you're symptomatic on levothyroxine and your provider is only checking TSH, the evaluation is incomplete. A thorough thyroid assessment includes:
| Marker | What It Shows |
|---|---|
| TSH | Pituitary signaling. Useful as a screening tool but insufficient on its own for patients with ongoing symptoms. |
| Free T4 | The inactive hormone produced by the thyroid gland. Shows what's available for conversion but not what's being converted. |
| Free T3 | The active hormone that cells actually use. A low Free T3 with a normal TSH explains why patients on levothyroxine still feel hypothyroid. |
| Reverse T3 | An inactive form that competes with active T3 at the receptor level. Elevated reverse T3 under chronic stress blocks the effect of whatever active T3 is available. |
| TPO and TgAb antibodies | Thyroid antibodies indicate autoimmune thyroid disease including Hashimoto's, which requires a different management approach than non-autoimmune hypothyroidism. |
When Levothyroxine Alone May Not Be Enough
For patients who don't convert T4 to T3 adequately, levothyroxine provides only half of what the thyroid system needs to function well. Some of these patients do better on a medication that includes T3 alongside T4.
Armour Thyroid is a naturally desiccated thyroid medication derived from porcine thyroid glands. It contains both T4 and T3 in addition to smaller amounts of T1, T2, and calcitonin. For patients whose conversion is genuinely impaired, having pre-formed T3 available bypasses the conversion step entirely.
Compounded NDT is a customized alternative for patients who want the T4/T3 combination without the dyes or additives in commercial preparations, or who need a dose that isn't available in standard tablet form.
A synthetic T4/T3 combination using levothyroxine plus liothyronine is another option, particularly for patients who avoid pork products for personal or religious reasons. While this can be effective, clinically many patients report more consistent symptom relief on natural desiccated thyroid than on synthetic combinations, though this varies considerably between individuals.
Comparing thyroid medication options
Not Everyone Does Better on NDT
Porcine thyroid contains a higher T3-to-T4 ratio than the human thyroid gland produces. For some patients, particularly those who are sensitive to T3 fluctuations, this can feel overstimulating and may cause palpitations, sweating, anxiety, insomnia, or loose stools. These side effects are typically dose-related and can often be managed with slower titration or by switching to a synthetic T4/T3 combination that allows more precise ratio control.
The right medication depends on conversion status, symptom profile, antibody status, and how the individual patient responds clinically. There is no universal answer, which is why the evaluation matters as much as the treatment decision.
Frequently Asked Questions
My TSH is normal but I still feel terrible on levothyroxine. What should I do?
Ask for a complete thyroid panel including Free T3, Free T4, reverse T3, and thyroid antibodies. A normal TSH with a low Free T3 is one of the most common findings in patients who are on levothyroxine and still symptomatic. It indicates that either conversion is impaired or that the dose is inadequate at the tissue level despite the pituitary appearing satisfied. This is worth evaluating rather than accepting as unexplained.
What is Armour Thyroid and is it better than levothyroxine?
Armour Thyroid is a naturally desiccated thyroid medication containing both T4 and T3 derived from porcine thyroid. It's not universally better than levothyroxine, but it can produce significantly better symptom relief for patients whose T4-to-T3 conversion is impaired. Whether it's appropriate for you depends on your conversion status, antibody picture, and clinical response, not a general preference for natural versus synthetic.
What is Hashimoto's and does it change the treatment approach?
Hashimoto's thyroiditis is an autoimmune condition in which the immune system attacks thyroid tissue. It's the most common cause of hypothyroidism and is diagnosed by elevated TPO or TgAb antibodies. Managing Hashimoto's involves not only thyroid hormone replacement but also addressing the inflammatory and immune environment driving the attack, which includes factors like gut health, nutrient status, and stress physiology. Knowing whether autoimmune disease is present changes the clinical picture meaningfully.
Can thyroid issues cause weight gain even when labs look normal?
Yes. Even mildly suboptimal Free T3 reduces resting metabolic rate, impairs fat utilization, and causes the kind of fatigue that reduces activity and worsens metabolic health. A patient with a normal TSH, adequate Free T4, and low-normal Free T3 may struggle significantly with weight despite doing everything right, and no one connects it to their thyroid because the standard test looks fine.
I avoid pork for religious or personal reasons. Can I still optimize my thyroid?
Yes. A synthetic combination of levothyroxine and liothyronine provides both T4 and T3 without animal-derived ingredients. It requires more precise titration than NDT, but it's a clinically valid option for patients who need T3 added to their regimen and cannot use porcine-derived products.
Where can I get a complete thyroid evaluation in Dallas?
We're at 5301 Alpha Road, Suite 34, Room 21, Dallas, TX 75240, near the Galleria. Telehealth is available across Texas and several additional states. Call us at 214-890-6180 or book through our website. Full thyroid evaluation is part of our standard hormone workup.
Thyroid Health · Dallas, TX
Normal labs are not the same as optimal thyroid function.
If you're on thyroid medication and still feel off, the answer may be in what hasn't been tested. A complete thyroid panel and a provider who knows what to do with it can change the conversation entirely.
Book a Consultation in DallasOr call us at 214-890-6180 · Telehealth available across TX, CO, FL, IA, VT, VA, WA, CT
