Thyroid hormone once hid in hamburger meat, and some supplements hide it now

Key takeaways

• In 1984 and 1985, ground beef made from neck trimmings that held cattle thyroid tissue gave 121 people in Minnesota, South Dakota and Iowa an illness caused by too much thyroid hormone.
• A 2022 case series and a 2025 meeting abstract describe people whose thyroid hormone levels shot up after taking supplements with animal thyroid or suspected hidden hormone; one woman’s heart raced in the 160s.
• Kelp and other seaweed can push a thyroid too low or too high, especially in people with Hashimoto’s disease, Graves’ disease or thyroid nodules.
• The FDA-approved levothyroxine label warns that thyroid hormone should not be used for weight loss, and that too much can trigger heart rhythm problems, most often atrial fibrillation in older adults.
• Bring every supplement bottle to thyroid appointments, since hidden hormone and biotin can both make thyroid blood tests misleading.

Starting in April 1984, doctors in neighboring parts of Minnesota, South Dakota and Iowa began seeing people with the same set of complaints¹. Patients couldn’t sleep. They felt nervous, sweated heavily, had headaches and lost weight².

Their thyroid hormone was running high. The outbreak lasted until August 1985¹. A Colorado State University teaching summary of the investigation puts the toll at 121 cases in nine counties².

The source was hamburger. A single slaughter plant had been making ground beef from neck trimmings, and those trimmings contained cattle thyroid tissue¹. Tests of the plant’s ground beef found high levels of thyroid hormone¹.

The investigators, who reported their work in the New England Journal of Medicine in 1987, concluded that eating the beef raised people’s own blood levels of the hormone¹. Animal thyroid, in other words, keeps working after you swallow it.

That lesson matters again. Animal thyroid now turns up in supplements⁴, and doctors suspect thyroid hormone hides in others⁵. Here is what “thyroid support” products can hold, what they have done to people, which nutrients matter, and how supplements can throw off thyroid tests and treatment.

A ban on “gullet trimming” didn’t end the problem

The meat-plant practice behind the outbreak had a name: gullet trimming. Because the thyroid sits in the neck, grinding neck meat can sweep the gland into hamburger or sausage². After the Midwest outbreak, gullet trimming was banned in U.S. plants that slaughter cattle and pigs²³.

A 2003 report in the Canadian Medical Association Journal (CMAJ) shows why the lesson lasts. Two Ontario doctors described a 61-year-old farm woman who had five bouts of an overactive thyroid over 11 years, each lasting two to three months³. Specialists had called it silent thyroiditis, a painless type of thyroid inflammation³¹².

The real cause was on her plate. The family raised its own beef, and the butcher who processed their cows didn’t know gullet trimming had been outlawed, so neck meat went into the patties she ate³. Her husband passed on the patties and had no thyroid trouble. The authors called the timing of her bouts after each slaughter highly supportive of hamburger thyrotoxicosis³.

Her blood had hinted at it. In her last bout, her free T4, a key thyroid hormone measure, was twice the top of the normal range by our math (46 versus 23)³. Her thyroglobulin, a thyroid protein, was low, a pattern doctors treat as a clue that hormone is coming from outside the gland³⁶.

The authors urged doctors to think of this cause in people who butcher their own animals and in hunters who trim game³. That’s no knock on home butchering, a skill many self-reliant families value. It’s a reminder to keep the gland out of the grind.

“Thyroid support” capsules have sent people to the hospital

Our hormone-balancing article describes a 2013 lab test that found thyroid hormone in most “thyroid support” products it checked. Case reports since then show what can happen to the people who take them.

In an abstract posted in April 2025 for a Society of Hospital Medicine meeting, two doctors from OhioHealth Riverside Methodist Hospital in Ohio described a 49-year-old woman who reached the emergency room after three weeks of swelling and weight loss⁴. Her pulse was in the 160s. Her free T3 was 13.0, nearly three times the top of the normal range by our math⁴.

The trail led to a new set of herbal pills. Shortly before, a functional medicine practitioner had put her on several, and a review of them found sheep thyroid hormone in one⁴. Once it was stopped and she was treated, her symptoms and lab results improved quickly, and she went home on day nine⁴.

Her workup also revealed underlying Graves’ disease, an autoimmune cause of an overactive thyroid⁴¹². A meeting abstract is a short report, not a full peer-reviewed paper, but it fits a long pattern.

Hidden hormone can come without any animal on the label. In 2022, doctors at Hospital Italiano de Buenos Aires in Argentina reported six people with factitious hyperthyroidism, meaning excess thyroid hormone that came from outside the body⁵. All six had taken weight-loss supplements, and the ones whose source was described had been bought online or imported from the U.S.⁵.

The labels listed L-tyrosine, L-carnitine, green coffee, yerba mate and “blueberry ketones,” with no hormone⁵. Yet the patients had very low TSH, and those whose T3 was measured ran high, a pattern the authors tied to swallowing T3⁵. The products weren’t chemically tested, so the hormone is suspected, not proven, and the doctors reported them to Argentina’s drug regulator⁵.

There’s older history too. Two Japanese diet products sold from 2000, Dream Shape and Ever Youth, were tied to 12 cases of thyrotoxicosis, or too much thyroid hormone, and both contained T3 and T4, according to a 2009 article in The Journal of Family Practice⁶.

The FDA has stepped in at least once. Triax Metabolic Accelerator, a so-called dietary supplement, got its kick from tiratricol (TRIAC), a compound with real thyroid-hormone strength, and in November 1999 the agency told consumers to avoid it⁷.

At the maker’s suggested dose, the American Thyroid Association said, many users could expect the effects of 100 to 200 micrograms of thyroxine a day⁷. A year later, the FDA warned that tiratricol products could cause heart attacks and strokes⁸.

Kelp can push a thyroid in either direction

The thyroid can’t make its hormones without iodine¹⁴. Kelp, dulse and other seaweeds can carry large amounts of it¹²¹³, and that’s where the trouble starts.

A healthy thyroid has a built-in brake. When a big dose of iodine arrives, the gland briefly slows hormone production, a response called the Wolff-Chaikoff effect, and the slowdown usually lasts a day or two before the gland adapts¹⁰.

In some people the brake sticks. A 2024 review in the journal Endocrine Reviews explains that after a sudden iodine load, susceptible people who fail to escape the Wolff-Chaikoff effect can end up with an underactive thyroid⁹. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says people with Hashimoto’s may be especially sensitive: for them, large amounts of iodine from seaweed or supplements can cause or worsen an underactive thyroid¹³.

Other people get the opposite. In what’s called the Jod-Basedow phenomenon, extra iodine fuels too much hormone, especially in a thyroid with nodules⁹¹⁰. NIDDK warns that seaweed and iodine supplements may cause or worsen an overactive thyroid, especially in people with Graves’ or other autoimmune thyroid disease¹².

Most people handle extra iodine well, the 2024 review notes⁹. The risk sits with people whose thyroids are already vulnerable. And the NIH Office of Dietary Supplements points out a twist: too much iodine can bring on some of the same problems as too little, including goiter, a swollen thyroid¹²¹⁴. Our iodine article covers safe amounts and why kelp doses are so unpredictable.

The nutrients with real thyroid jobs are few

Wanting to nourish your thyroid with food and plants is a sound instinct. The gland depends on iodine from your diet¹⁴, and our iodine article lists the foods that supply it.

Researchers are studying selenium, along with vitamin D, in Hashimoto’s disease, but NIDDK says no specific guidance exists yet¹³. Our selenium article weighs the trials and its narrow safe range.

L-tyrosine, an amino acid, shows up on some “metabolism” and weight-loss labels, including the Argentine products above⁵. Our search of NIH and journal sources turned up no clinical trials showing that extra tyrosine raises thyroid hormone in people. Ashwagandha, the Ayurvedic herb, has its own case reports of thyroid hormone climbing too high, covered in our ashwagandha article.

This is where the instinct gets exploited. A product that truly moves thyroid hormone levels is acting like a drug, and with a drug, the dose is everything.

The honest version of natural thyroid support looks different: iodine from food, a real diagnosis, and, if you need hormone, a measured dose checked with follow-up blood tests¹¹. That respects both your body and your right to know what you’re swallowing. If you suspect a thyroid problem, ask for blood tests, since symptoms alone can’t diagnose it¹²; our thyroid article explains the results.

Supplements can scramble thyroid tests and treatment

Hidden hormone also changes the numbers doctors use to make decisions.

In the Argentine series, one woman already took levothyroxine, the standard thyroid pill, for an underactive thyroid. Her test results made her look overtreated, so her prescription dose was cut, yet her TSH stayed suppressed⁵. Once the weight-loss product was out of the picture, she needed her usual dose again⁵.

The Canadian farm woman’s bouts were misread for years³. Tiratricol can even register as T3 on some lab tests, the American Thyroid Association notes, which muddies results further⁷.

Two other supplement problems appear on the FDA-approved levothyroxine label:

• Biotin. This B vitamin can interfere with lab tests for TSH, T4 and T3. The label’s advice is to pause biotin-containing supplements at least two days before testing¹¹. Our vitamins field guide explains why.
• Absorption. Calcium, iron and some foods can keep levothyroxine from getting in, as our medicine-spacing article explains. The label adds that grapefruit juice may delay absorption and lower how much reaches your blood¹¹.

The label also carries a boxed warning headed “Not for treatment of obesity or for weight loss,” adding that larger doses can cause serious or even life-threatening toxicity¹¹. Three of the product groups above were sold for weight loss⁵⁶⁷.

Who should be most careful

• People with Hashimoto’s disease. Large amounts of iodine can worsen an underactive thyroid¹³.
• People with Graves’ disease or another autoimmune thyroid condition. Seaweed and iodine supplements may worsen an overactive thyroid¹². The woman in the 2025 case turned out to have Graves’ disease underneath her supplement problem⁴.
• People with thyroid nodules or goiter. Extra iodine can push a nodular gland into making too much hormone¹⁰.
• Pregnant women. Too much iodine can cause goiter in the baby¹³, and a severe, untreated overactive thyroid can affect mother and baby¹². Thyroid medicine needs can also rise in pregnancy, which is one reason testing matters¹¹.
• Older adults. An overactive thyroid can cause an irregular heartbeat that leads to clots and stroke, and in older adults it can pass for depression or dementia¹². When older patients get too much levothyroxine, atrial fibrillation is the rhythm problem seen most often, its label says¹¹.
• Postmenopausal women. Too much levothyroxine can thin bones, particularly after menopause, the label says¹¹.
• Anyone on thyroid medicine. Hidden hormone stacks on top of a prescription⁵, and high-dose iodine can push hormone too low in people taking antithyroid drugs such as methimazole¹⁴.

The thyroid supplement label check

Our own tool, built from this article’s sources. Read the Supplement Facts panel and the full ingredient list, then find each ingredient below.

If the label lists	What it can do	Main risk	Evidence
“Thyroid,” “raw thyroid,” “thyroid glandular,” or bovine, porcine or ovine (sheep) thyroid	Deliver active thyroid hormone in an unknown dose14	Overactive thyroid, racing heart, misleading tests34	Evidence says no, or unsafe
A “metabolism” or “thyroid support” blend with no hormone listed	May still hide hormone, as doctors suspected in Argentina5	Same as above5	Evidence says no, or unsafe
Tiratricol or TRIAC	Acts as a thyroid hormone7	The FDA warned of heart attack and stroke8	Evidence says no, or unsafe
Kelp, dulse, other seaweed or iodine	Supplies iodine, needed in small amounts14	Can tip a vulnerable thyroid low or high1213	Evidence says no, or unsafe as a booster
L-tyrosine	An amino acid; our search found no trials showing it raises thyroid hormone	Little known on its own; check what else is in the blend5	Not enough evidence
Selenium	Under study in Hashimoto’s13	Narrow safe range; see our selenium article	Promising but early
Biotin	Can skew TSH, T4 and T3 lab tests11	False thyroid results11	Strong evidence of test interference

How strong is the evidence?

Use or claim	Evidence level	Why
Getting enough iodine from food for thyroid hormone	Strong evidence	The gland needs iodine to make its hormones14
Glandular or “thyroid support” products to boost a slow thyroid	Evidence says no, or unsafe	Documented cases of an overactive thyroid from animal thyroid and suspected hidden hormone1345
Kelp or iodine supplements as a thyroid booster	Evidence says no, or unsafe	Can cause or worsen under- and overactive thyroid in susceptible people91213
Tiratricol (TRIAC) or thyroid hormone for weight loss	Evidence says no, or unsafe	FDA warning; boxed warning on the levothyroxine label7811
L-tyrosine to raise thyroid output	Not enough evidence	Our search found no human trials of it for this
Selenium for Hashimoto’s disease	Promising but early	Still being studied; no guidance yet13
Biotin distorting thyroid blood tests	Strong evidence	Named on the FDA-approved label11

When to get help

• See a clinician soon if you notice signs of too much thyroid hormone after starting a supplement: a racing or irregular heartbeat, shakiness, trouble sleeping, sweating or heat intolerance, or weight loss despite a bigger appetite¹².
• Talk with a clinician first about kelp, seaweed or iodine products if you have Hashimoto’s, Graves’ disease or nodules, or are pregnant¹⁰¹²¹³.
• If you take thyroid or antithyroid medicine, tell your prescriber about every supplement, including over-the-counter products, as the levothyroxine label asks¹¹¹⁴.
• Get medical help promptly if a fast or irregular heartbeat comes with chest pain or shortness of breath. The levothyroxine label tells patients to report these symptoms¹¹, and the 2025 patient’s racing heart and swelling ended in a hospital stay⁴. Our thyroid article lists the signs of thyroid storm, an emergency.
• If someone swallows a large amount of thyroid medicine or a hormone-containing product, call Poison Control at 1-800-222-1222. The label notes that symptoms may not show up for several days¹¹.

If you think a supplement harmed you, the FDA directs consumers to report it through its Safety Reporting Portal¹⁵. Keep the bottle and its lot number.

Questions readers ask

The bottom line

Animal thyroid tissue made 121 people sick when it slipped into hamburger, and it can do the same in a capsule. The “thyroid support” products that change thyroid levels do it with hormone or iodine in a dose the label doesn’t state, and they can mislead the tests your clinician relies on.

Feed your thyroid with food iodine, get a real diagnosis when something feels off, and let any hormone you take come with a known dose and follow-up tests. Bring every bottle to your appointments.

Related reading

• Real hormone problems have names and tests, which “balance your hormones” claims lack
• A slightly high thyroid number often needs watching, not a pill
• Iodine Is Slipping in American Diets. Kelp Pills Are the Wrong Fix
• What gets into supplements that isn’t on the label
• Home hormone tests can answer some questions, but the “egg timer” test can’t

Sources

1. Hedberg CW, Fishbein DB, Janssen RS, et al. “An outbreak of thyrotoxicosis caused by the consumption of bovine thyroid gland in ground beef.” New England Journal of Medicine, 1987;316(16):993-998 (FAO AGRIS record with abstract). agris.fao.org
2. Colorado State University, VIVO Pathophysiology (Hypertexts for Biomedical Sciences). “Hamburger Thyrotoxicosis.” Accessed October 2026. vivo.colostate.edu
3. Parmar MS, Sturge C. “Recurrent hamburger thyrotoxicosis.” CMAJ, 2003;169(5):415-417. cmaj.ca
4. White CJ, Parsley E. “Supplement-induced Thyrotoxicosis: An Unexpected Endocrine Storm.” Society of Hospital Medicine Converge 2025, Abstract 0839 (meeting abstract), posted April 23, 2025. shmabstracts.org
5. Varsavsky M, Ortiz MI, Lovazzano S, Scheinfeld G, Rubino GC, Kozak A. “Hipertiroidismo facticio por ingesta de suplementos herbales para reducción de peso” (Factitious hyperthyroidism from herbal weight-loss supplements). Medicina (Buenos Aires), 2022;82(6):974-977. medicinabuenosaires.com
6. Taylor T, Czarnowski C. “Asymptomatic hyperthyroidism.” The Journal of Family Practice, 2009;58(4):203-206. cdn.mdedge.com
7. American Thyroid Association. “ATA Supports FDA Warning on Triax.” February 26, 2000. thyroid.org
8. SupplySide Supplement Journal (trade press; cited for events only). “FDA Warns Consumers About Thyroid Hormone Supplement.” November 22, 2000. supplysidesj.com
9. Sohn SY, Inoue K, Rhee CM, Leung AM. “Risks of Iodine Excess.” Endocrine Reviews, 2024, doi:10.1210/endrev/bnae019 (Endocrine Society abstract page). endocrine.org
10. Khudair A, Khudair A, Niinuma SA, Habib H, Butler AE. “Beyond thyroid dysfunction: the systemic impact of iodine excess.” Frontiers in Endocrinology, 2025;16:1568807. frontiersin.org
11. Neolpharma, Inc. “LEVO-T (levothyroxine sodium) tablets: Prescribing Information.” FDA-approved label, revised May 2026. accessdata.fda.gov
12. National Institute of Diabetes and Digestive and Kidney Diseases. “Hyperthyroidism (Overactive Thyroid).” NIH, last reviewed August 2021. niddk.nih.gov
13. National Institute of Diabetes and Digestive and Kidney Diseases. “Hashimoto’s Disease.” NIH, last reviewed June 2021. niddk.nih.gov
14. NIH Office of Dietary Supplements. “Iodine: Fact Sheet for Consumers.” Updated July 28, 2022. ods.od.nih.gov
15. U.S. Food and Drug Administration. “How to Report a Non-Emergency.” Content current as of March 29, 2018. fda.gov