An unusual about-face that played out at the Food and Drug Administration over the last week illustrated the power of the “Make America Healthy Again” movement, particularly with its focus on “natural” drugs.
Last Thursday, the agency published a statement saying it had concerns about the safety and effectiveness of unapproved thyroid medications made from animal tissue after it received complaints from patients and reports of adverse events. As a result, the FDA said it had notified drugmakers of its “intent to take action” against the products, but added that it wouldn't do so immediately to give patients time to switch medications.
“The agency urges patients taking these unapproved animal-derived thyroid medications to treat hypothyroidism to talk to their doctor,” it wrote.
The statement in and of itself was nothing surprising. Warnings about unapproved drugs are standard fare for the FDA. What followed also wasn’t unheard of: social media backlash.
But on Wednesday evening, FDA Commissioner Marty Makary seemingly reversed course, writing in a post on X that the FDA was committed to pursuing the first-ever approval of desiccated thyroid extract, pending results of the ongoing clinical trials. “In the mean time, we will ensure access for all Americans,” he wrote.
Five minutes later, Health Secretary Robert F. Kennedy Jr. responded. “Love your approach of using gold standard science and common sense, @DrMarkaryFDA,” Kennedy wrote.
So, what was this all about?
Animal-derived thyroid pills
The thyroid — a small, butterfly-shaped gland located at the front of the neck — helps regulate how the body uses energy by producing thyroid hormones. When it doesn’t produce enough, it can lead to hypothyroidism, which can cause symptoms including unexplained weight gain, tiredness, sensitivity to cold, changes in menstrual cycles and symptoms of depression and anxiety, according to the Mayo Clinic. The condition is more common in women than men.
The standard treatment is prescription thyroid hormone replacement therapy — basically, taking pills that contain the needed thyroid hormones. Typically one of two synthetic hormones, levothyroxine or liothyronine, or a combination of both, are prescribed.
Some patients, however, turn to animal-derived thyroid pills either because they don’t respond well to the synthetic versions or want to take something marketed as natural, said Dr. Michael Weintraub, an endocrinologist at NYU Langone Health in New York City.
The pills — which aren’t FDA-approved — are made from dried thyroid glands, usually from pigs, and are sold under brand names like Armour Thyroid, NP Thyroid, Nature-Thyroid and Natural Thyroid, according to the agency.
About 1.5 million people in the U.S. were prescribed animal-derived thyroid pills in 2024, the FDA said.
In the FDA statement warning against the animal-derived drugs, the agency said they may contain impurities that could result in infections and could also contain inconsistent levels of thyroid hormones, another risk for patients. Taking too much can cause unwanted effects, the FDA said, and too little could not be effective.
The backlash
In the days that followed the FDA’s statement, patients and doctors took to social media to voice their opposition.
“BREAKING FDA set to BAN natural desiccated thyroid medications. Millions rely on these for hypothyroidism who don’t respond well to synthetic thyroid pharmaceuticals,” read one post from Will Cole, a functional medicine doctor. “Let your voice be heard. The FDA needs to change course on this one.”
Dave Asprey, the founder of Bulletproof Coffee, a coffee and supplement brand, wrote: “I found out I had very low thyroid levels in my mid-20s, and Hashimoto’s. Normal synthetic thyroid drugs did not work. Natural thyroid extract worked very well and I have been taking it for more than 25 years without a problem.”
Dr. Robert Malone — an anti-vaccine activist who was recently appointed by Kennedy to a vaccine advisory panel — called the decision “terrible news — particularly for postmenopausal women.” He called on doctors and patients to contact the FDA in response.
Andrew Nixon, a spokesperson for the Department of Health and Human Services, did not respond to a question about whether Makary’s post on Wednesday was in response to social media backlash.
When asked about whether the FDA would still take action against unapproved thyroid products, Nixon referred NBC News to the agency’s statement last week, which said, “FDA is not taking immediate action against manufacturers who make unapproved animal-derived thyroid medication to give patients time to transition to an FDA-approved medication to treat their hypothyroidism.”
Nixon added that the agency “will share additional information as it becomes available and as clinical trial results are released.”
It’s unclear which ongoing trials Makary and Nixon were referring to. ClinicalTrials.gov lists a trial initiated by Walter Reed National Military Medical Center in 2012, but the trial’s status is currently marked as “unknown.” Allergan, the maker of Armour Thyroid, completed a trial in 2021 comparing its product to levothyroxine, a synthetic thyroid hormone.
So, are these pills safe?
Dr. Pieter Cohen, an associate professor of medicine at Harvard Medical School, said the FDA was correct to issue its initial warning about the thyroid pills, noting that the animal-derived pills aren’t regulated by the agency and can pose significant risks.
The FDA-approved synthetic versions usually replace one of two thyroid hormones: T4, the main hormone the thyroid produces, or T3, the active form of T4 that helps regulate energy and metabolism. Companies that make FDA-approved drugs must follow certain regulations, including consistent dosing.
The animal-derived versions also contain the thyroid hormones, just like prescription medications, Cohen said, but because they’re unregulated, the amount they contain can be all over the place.
“Getting too much or too little thyroid hormone has long-term health risks,” he said. “If you take too much, it can damage your bones, it can damage your heart. If you take too little, if you’re not getting enough, a number of problems can occur too, including mood problems, like depression.”
Weintraub, of NYU Langone Health, said that tiny changes in thyroid hormone levels can have a big impact, so it’s important to get the dosage right. He noted that pigs naturally have much higher levels of T3 than humans.
“It can lead to heart rhythm disturbances, which can be life-threatening. It can lead to bone degradation, which can lead to broken bones,” he said.
Weintraub said he’s had patients who took animal-derived thyroid pills who’ve had issues with sleeping, had sensitivity to heat or developed osteoporosis.
Dr. Susan Spratt, an endocrinologist and senior medical director for the Population Health Management Office at Duke Health in North Carolina, however, said that it would be unfair for the FDA to “suddenly yank” the animal-derived versions from the market “without dedicated reasons that they are harmful.”
Spratt said that the animal-derived pills have been around for decades as a prescribable drug. (Weintraub said the animal-derived drugs were “grandfathered in,” meaning they were already on the market before current FDA standards for safety were put into place.)
While Spratt said she prefers to prescribe the FDA-approved synthetic versions, the animal-derived versions offer an option for people who don’t respond well to the synthetic ones.
“I would welcome NIH funding on why some patients don’t feel as good on T4-only products,” she said.
Weintraub said the synthetic versions don’t “necessarily help everyone’s symptoms, but there’s a more precise and safer way of treating that than resorting to a pig or cow thyroids.”
He said patients who don’t respond well to T4- or T3-only medications often do better on a combination of the two.
