The Best Time to Take Levothyroxine — And Why American Doctors Are Getting It Wrong

Jennifer Margulis, PhD

A version of this article was first published on Jennifer Margulis’s

Substack, Vibrant Life 

I was contacted recently by a reader I’ll call J.P.

As he explained when we talked on Zoom, J.P. spent nearly four years battling symptoms related to mismanaged hypothyroidism.

Hypothyroidism

Hypothyroidism is a condition where the thyroid—a butterfly-shaped gland at the front of the neck—doesn’t make enough thyroid hormone. This medical issue is also called “underactive thyroid.”

In its early stages, hypothyroidism may not cause obvious symptoms. However, it can become severe, leading to even more serious health problems, such as heart issues, extreme lethargy, and breathing problems if left untreated.

Tired, depressed, and apathetic

J.P.’s presenting symptoms included feeling constantly tired, depressed, and apathetic.

In J.P.’s case, brain fog became a part of his daily life. His creative drive all but disappeared, his analytical reasoning dulled. He started feeling tired in a bone-crushing way that sleep couldn’t fix.

Perplexed as to why the activities that had always been so automatic started taking him an incredible amount of effort, he knew he needed a definitive answer to what was wrong. He longed to be himself again.

But even though he’d had a thyroidectomy some years before and his presenting symptoms were a clear indication that the thyroid medicine he was on was not doing its job, no one was sure what to do. The doctors tried increasing the dosing and changing his thyroid medication to one that was more easily absorbed.

Nothing helped.

J.P. started doubting himself. Though he felt terrible, maybe nothing was wrong?

Maybe being exhausted and foggy was just his new normal? Since nothing was working, maybe the problem wasn’t fixable?

Elevated blood levels of TSH are a sign of hypothyroidism. J.P., a successful investor, had over 30 lab results spanning three years and nine months that documented elevated thyroid stimulating hormone. Yet his doctors kept telling him to “follow the standard morning protocol” despite the fact that it was not working.

So when is the best time to take levothyroxine?

The conventional treatment for hypothyroidism is usually a daily dose of an artificial thyroid hormone, the most common of which is called levothyroxine.

Every physician J.P. saw told him the same thing: levothyroxine first thing in the morning. On an empty stomach. Then wait 30 to 60 minutes before eating.

This was dogma, repeated in every prescribing guideline, every patient handout, every endocrinology textbook.

But J.P. had followed his doctors’ instructions perfectly, but these instructions left him chronically ill.

Exhausted and at a loss, J.P. realized he needed to figure out why his body wasn’t responding to the medication, even at increased doses.

Simply put, he was not getting well.

So started reading as much as he could in the scientific literature.There had to be an answer somewhere. He read papers on malabsorption. Among other things, he discovered that even separated by more than an hour from dosing, coffee interferes with thyroid hormone absorption.

He ordered his own duodenal biopsies looking for causes of malabsorption. He went on special diets. He fasted. Then he started eating just one meal a day.

Absolutely nothing worked. He was wretched, depressed, and under-functioning. Then, on a whim born of desperation, J.P. thought: maybe I should just try taking levothyroxine at bedtime.

One week after he changed from morning dosing to bedtime dosing, his TSH normalized.

For the first time in almost four years, he felt like himself again.

American doctors mismanaging thyroid medication administration?

J.P. believes that American doctors are catastrophically mismanaging thyroid medicine administration.

The American Thyroid Association’s dismisses the idea that bedtime dosing can be effective for some patients, dubbing it only a “weak recommendation” based on limited evidence.

Europe recommends bedtime dosing

At the same time, the European Thyroid Association (ETA), reviewing newer clinical evidence, has issued a “strong recommendation” for bedtime dosing.

In its most recent guidelines, issued in 2025, the ETA asserts that bedtime dosing is therapeutically equivalent to morning dosing.

While doing his own research, J.P. also discovered a landmark randomized double-blind study, conducted in 2010, that found significant benefits to bedtime dosing. Yet the American Thyroid Association insists on a morning-only dosing protocol. In other words, some 30 million American patients are being told to follow a timing protocol that does not work.

The European Thyroid Association, on the other hand, recommends that hypothyroid patients choose the timing that is best for their own lifestyle.

Doubling down on ill-timed dosing

Though the evidence and guidelines have changed, American doctors continue telling patients the same thing they have been saying for decades.

J.P. told me that he feels that doctors are not giving patients options and are instead fundamentally rejecting a hypothyroid patient’s freedom to choose.

An unwillingness to offer bedtime dosing as an option, J.P. contends, is harming hundreds of thousands of people with hypothyroidism and unnecessarily perpetuating—even causing—related health problems.

Hypothyroid pregnant women and their unborn babies vulnerable to harm

Three of my acquaintances, that I know of, had total thyroidectomies as young adults to treat autoimmune disease. All three wanted biological children. None was able to carry a baby to term. Until I started talking to J.P., I thought their fertility issues had to do with their struggles with autoimmunity. Now I wonder if the miscarriages had more to do with medical mismanagement than with the autoimmune disease.

This isn’t just about tired middle-aged men who can’t get their doctors to listen. This dosing timing issue is also affecting pregnant women and their unborn babies.

The fetal brain depends entirely on maternal thyroid hormone from weeks 5-14 of gestation.

After week 14, the damage is irreversible.

A 2019 MRI study by Jansen showed this: maternal TSH affects brain structure only when measured at 8 weeks. By 14 weeks, the association disappears.

This is the equivalent of the critical window for preventing neural tube defects by making sure a pregnant woman is eating foods rich in folate (leafy greens, black beans, cruciferous vegetables, nuts, and some fruits) and supplementing with methyl-folate. In both cases—to avoid neural tube defects in the fetus and hypothyroid-induced miscarriage or other health issues—there is a narrow biological window for prevention. Miss it, and the damage cannot be repaired, no matter how much intervention comes later.

Yet American guidelines for managing hypothyroidism during pregnancy recommend against early screening based on two major trials (CATS 2012, Casey 2017) that started treatment at 13-18 weeks. After the critical window for brain development has already closed.

The trials tested whether late treatment could rescue damage already done.

It could not. So the American medical establishment concluded thyroid treatment in pregnancy doesn’t work.

In the meantime, a 1990 study by Mandel showed that 75 percent of treated hypothyroid women see their TSH spike as early as week 6 without dose adjustment.

Every pregnant woman is told to take prenatal vitamins, many of which contain iron and calcium. Iron and calcium reduce levothyroxine absorption by 20-30 percent when taken within four hours.

FDA label for Synthroid (levothyroxine) warns about “iron supplements” and “calcium supplements.” It explicitly recommends that users “separate administration of these agents from levothyroxine by at least four hours.”

But the FDA’s instructions do not explicitly mention “prenatal vitamins” or that prenatal vitamins can directly interfere with thyroid medications.

This is a critical omission because pregnant women think of a stand-alone iron supplement as a separate pill, not an ingredient in their prescribed or over-the-counter prenatal vitamins.

So expectant moms take both in the mornings, the medicine is not absorbed, and the fetal brain suffers during the exact weeks when it is developing rapidly and most vulnerable to damage.

A 1999 study showed untreated maternal hypothyroidism causes a 7-point IQ deficit in children. The FDA knows this. It’s in their medical reviews written in 1999. They documented that inadequate treatment causes miscarriage and fetal harm. Yet their warnings about iron and calcium don’t mention prenatal vitamins.

It felt like someone washed the windows

J.P. told me that when he finally discovered that bedtime dosing worked for him, everything changed. His TSH normalized. His energy returned. His brain fog lifted. His sense of self came back.

A systems failure

But J.P.’s one person.

What about the hundreds of thousands of hypothyroid patients, including pregnant women, whose disease is being mismanaged?

These patients are being told to follow a dosing protocol that is demonstrably less effective, for the subclinical cohort, than what the European Thyroid Association recommends.

Among pregnant women, 2 to 5 percent have subclinical hypothyroidism. The American College of Obstetricians and Gynecologists (ACOG), does not recommend universal screening.

If even a fraction of pregnancies were affected by delayed screening due to ACOG’s guidelines against universal screening, and if bedtime dosing could have prevented some of the preventable miscarriages and developmental delays, the scale of harm is staggering.

J.P. contends that this medical mismanagement is leading to the miscarriages, children born with preventable cognitive impairment, and women being told—like J.P. was—that the problems are all in their head, that their symptoms aren’t real, and that they just need to “reduce the stress in their lives.”

In other words, we’re not talking about one man’s three-year struggle. We’re talking about millions of pregnancies resulting in avoidable miscarriages and brain dysfunction in offspring - that just comes down to the best time to take levothyroxine.

A man on a mission

J.P. is no longer waiting for the system to fix itself. He’s filing a federal lawsuit. He’s alleging that certain authorities failed to update levothyroxine labels to include bedtime dosing as a viable alternative despite clinical evidence supporting its efficacy. He’s arguing that this omission represents a labeling deficiency.

He’s building a case using rigorous analysis of competing hypotheses, systematically processing the clinical literature to demonstrate that the manufacturers had access to evidence they chose not to disclose. He’s not asking for permission from the system anymore. He’s forcing the system to answer.

If you’re a hypothyroid patient with a story or a pregnant woman whose thyroid dysfunction was mismanaged, J.P. would like to hear from you. Contact him at levolawsuit@proton.me.

Your story matters. The evidence matters. And it’s time the medical establishment caught up to what Europe already knows.

About the author: Jennifer Margulis, Ph.D., is an award-winning science journalist, Fulbright grantee, and sought-after speaker.

She writes a popular Substack that has over 20,000 subscribers, Vibrant Life, and is a regular contributor to The Epoch Times. A different version of this article first appeared in print in the magazine Radiant Life.

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