On levothyroxine and still not right — _what gets in the way_

You were diagnosed, you were given levothyroxine, and the first stretch of it helped. Then it stopped helping, or it never fully did. Your TSH comes back in range — your prescribing doctor says the dose is right — and you are still cold, still flattened by mid-afternoon, still losing hair in the shower, still constipated, still waiting to feel like the person you were before any of this started. The lab says treated. Your body says otherwise.

This is one of the most common conversations we have, and it is rarely about willpower or about the medication being the wrong choice. Levothyroxine is T4 — a storage form. For it to do anything, it has to survive the stomach, cross the gut wall, travel bound to protein, and then be converted inside your tissues into T3, the form that actually binds the receptor. There are several places that chain can fail quietly while TSH still looks obedient. We don’t mask symptoms — we look to address the underlying issues that cause symptoms and dis-ease, and with a medicated thyroid that usually means examining the steps between the tablet and the cell.

Why TSH can look fine while you don’t

TSH is made by the pituitary, and the pituitary is an unusual tissue. It generates its own local T3 from circulating T4 using type 2 deiodinase, which it has in abundance. That means the pituitary is exquisitely sensitive to T4 — the exact thing you are swallowing every morning. Give enough T4, and the pituitary is satisfied and quiets TSH down, regardless of how much T3 your liver, muscle, gut, and brain are actually producing from that same T4.

So a normal TSH on levothyroxine confirms one thing with certainty: the pituitary is getting enough. It is weaker evidence about the rest of you. This is why we want the whole panel rather than a single number — free T4, free T3, reverse T3, and antibodies — which we go through in more detail in normal TSH, still exhausted. The pattern we are looking for in a medicated patient is specific: free T4 comfortably mid-range or high, free T3 sitting at the floor of the range, TSH suppressed or low-normal. That combination says the T4 is arriving and not being converted. A different pattern — free T4 low along with free T3 — points back toward the gut, toward absorption.

Step one: the tablet has to actually get in

Levothyroxine is absorbed mostly in the jejunum and upper ileum, and the tablet needs an acidic stomach to dissolve properly first. Anything that raises gastric pH, binds the molecule, or damages the absorptive surface will cut the fraction that makes it into circulation. None of this is exotic. Most of it is sitting on your kitchen counter.

• Coffee. Taken close to the tablet, coffee measurably reduces levothyroxine absorption. For a lot of people this is the single biggest variable, and it is also the one nobody warned them about.
• Calcium and iron. Calcium carbonate and ferrous sulfate form poorly soluble complexes with levothyroxine in the gut. A morning multivitamin, a calcium supplement, or an iron tablet taken alongside the thyroid dose can meaningfully blunt it.
• Acid-suppressing medication. Proton pump inhibitors and H2 blockers raise gastric pH, and dissolution suffers. This is not a reason to stop anything — it is a reason for your prescribing doctor to know you are on both.
• Low stomach acid on its own. Age, chronic stress, and atrophic gastritis all reduce acid output without any medication involved. We wrote about why that gets misread as reflux in the acid question.
• H. pylori and gastritis. Chronic H. pylori infection and the atrophic gastritis that can follow are well documented causes of rising levothyroxine requirements.
• Celiac disease and intestinal damage. Villous atrophy reduces the absorptive surface itself. Celiac is also more common in people with autoimmune thyroid disease, which makes it worth ruling in or out rather than assuming.
• Fiber, soy, and bile acid binders. High-fiber supplements, soy protein, and resins such as cholestyramine all bind thyroid hormone in the lumen and carry it out with them.

We are not telling anyone to drop a supplement or a prescription. We are mapping what is being taken, and when, so the picture is complete before anybody concludes a dose is insufficient.

Step two: T4 has to become T3

Conversion is done by the deiodinase enzymes. Type 1 works largely in liver and kidney, type 2 in brain, pituitary, muscle, and brown fat, and type 3 does the opposite job — it inactivates, producing reverse T3. All three are selenoproteins. Each carries selenocysteine at its active site, which means selenium status is not a wellness talking point here, it is a structural requirement for the enzyme to function. Zinc matters too, both for deiodinase activity and for the thyroid hormone receptor’s ability to bind DNA once T3 arrives.

Beyond the minerals, conversion is sensitive to context. Sustained high cortisol pushes activity away from T3 and toward reverse T3. So do inflammatory cytokines — this is the familiar pattern seen in any significant illness, where the body deliberately downshifts metabolic rate. Prolonged low-calorie dieting does the same. Iron deficiency is a separate problem that often travels alongside, which is why we check ferritin in nearly every thyroid workup; the low ferritin, normal hemoglobin picture explains a lot of hair loss and fatigue that gets wrongly attributed to the thyroid dose.

A number in range tells you what the pituitary thinks. It does not tell you what the tissue is receiving. — Dr. Johanna Nazzar

Reverse T3, and the question it answers

Reverse T3 is an inactive mirror image of T3. It occupies the receptor without switching it on. It is produced normally, and an isolated elevated value does not diagnose anything by itself — we want to be clear about that, because reverse T3 gets oversold online. What it is useful for is as a direction marker. When free T4 is ample, free T3 is low, and reverse T3 is high, that pattern suggests the body is routing T4 down the inactivation pathway, and it prompts the real question: why. Inflammation, cortisol load, low selenium or zinc, poor liver function, chronic infection, and undereating are the candidates we work through, often with a nutrient panel rather than guesswork.

TSH-guided review versus symptom-guided review

Standard endocrine care titrates to TSH. That is a reasonable, evidence-based approach and it works well for a large number of people. Our role is different and sits alongside it: we look at the whole panel in functional ranges rather than only the regular laboratory ranges, and we weigh what you are reporting with equal seriousness. Patient care rather than disease care. If free T3 sits at the bottom of the range while your body temperature, bowel transit, hair, and energy all say undertreated, that is information worth putting in front of your prescribing doctor — not a reason for us to adjust anything.

Two testing details matter for this to mean anything. Draw blood before the day’s dose, not after, or free T4 will read artificially high from the peak. And biotin — common in hair and nail supplements — interferes with many thyroid immunoassays and can distort both TSH and free T4; pause it before testing exactly as the lab instructs.

The spacing habits we talk through

• Consistency over perfection. Take it the same way every day. A fluctuating routine produces fluctuating labs, which produces dose changes chasing noise.
• Move coffee off the dose. Not gone — just separated from the tablet. For some people this alone changes their numbers.
• Minerals at the other end of the day. Calcium, iron, and magnesium belong well away from the thyroid dose, typically in the evening.
• Tell the prescriber about acid suppression. If a PPI is part of your regimen, your dose was set in that context, and changes to it should be made with your prescribing doctor.
• Rule the gut in or out. Celiac serology, H. pylori testing, and a look at digestive function are reasonable steps when absorption is in question — the thyroid and the gut are more tightly linked than most people are told, as we covered in the gut–thyroid connection.

What else is usually in the room

If the underlying cause is Hashimoto’s — and in this country it usually is — then the immune process continues regardless of how well the hormone is replaced. Antibody activity, gut permeability, and inflammatory load are all part of why two people on an identical dose feel entirely different. That is a longer conversation, and we took it up separately in Hashimoto’s is an immune story.

Chinese medicine reads this same picture through a different lens — commonly Spleen and Kidney Yang deficiency, with its cold limbs, heavy fatigue, morning sluggishness, and loose or stubborn bowels. Acupuncture and herbs do not replace thyroid hormone and we never suggest they could. What they can support is digestive function and the stress load that drives conversion the wrong way.

Where we start

A first visit here is mostly collecting all the pieces of the puzzle: the full history, every medication and supplement with its timing, the complete thyroid panel drawn correctly, ferritin, selenium and zinc status, inflammatory markers, and a hard look at digestion. From there we can usually say which of the two failures — absorption or conversion — is the likelier one, and what would need to change to test that.

Any dose decision stays with your prescribing doctor. What we can bring to that conversation is a more complete set of data than a single TSH, and a clear account of what your body is actually reporting. If that is where you are, get in touch and we will start with the panel.

The journal is written by Dr. Nazzar from the practice. Articles reflect clinical observation and current research, not personalized medical advice. To explore your own case, schedule a consultation.