Desiccated thyroid extract (DTE), derived from animal thyroid glands, was once the primary treatment for hypothyroidism. While synthetic levothyroxine has become the preferred standard, DTE remains in use. This article examines the benefits and risks associated with DTE, provides an overview of current research, and clarifies recommendations for its use.
Understanding Hypothyroidism and Thyroid Hormone Replacement
Hypothyroidism, or an underactive thyroid gland, affects approximately 2% of the adult population in the United States. It occurs when the thyroid gland doesn't produce enough thyroid hormone, requiring lifelong treatment with thyroid hormone pills. Untreated hypothyroidism is associated with various symptoms, including nonspecific issues like memory problems, depression, and weight gain.
Levothyroxine, a synthetic form of the main thyroid hormone produced by the thyroid gland, is the most common replacement therapy. Before levothyroxine, desiccated animal thyroid extract was the only option. DTE is derived from dried and ground animal thyroid glands, usually porcine (from a pig). Some individuals prefer DTE, viewing it as a more "natural" thyroid hormone. Some patients who continue to experience hypothyroid symptoms while taking levothyroxine report improvement when switched to DTE.
Desiccated Thyroid Extract: Composition and Concerns
Thyroid extract comes from tissue in the animal thyroid gland and contains the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which are involved in many processes in the body.
FDA has concerns with the safety and effectiveness of the unapproved animal-derived thyroid medications, which have not been reviewed by FDA to ensure safety, purity and potency, and may have quality and dosing issues. Tablets made from the same manufacturing batches may not always provide the same thyroid hormone levels. Inconsistent doses can have serious consequences for patients. Too much medication can cause unwanted effects, and too little could not be effective. Thyroid medications derived from animal thyroid glands have an increased risk of certain impurities due to the source - animal thyroid tissue - or the way it is manufactured. These issues can lead to infections and other health concerns. The agency has received complaints from patients and reports of adverse events related to the safety and potency of these unapproved medications.
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Research Findings: DTE vs. Levothyroxine
Several studies have compared DTE to levothyroxine in treating hypothyroidism. A randomized, double-blind, crossover study by Hoang TD et al. (2013) involved 70 patients with hypothyroidism. Participants were treated with either DTE or levothyroxine for 12 weeks, then switched to the other treatment for 16 weeks. The participants were "blinded" during both phases - they did not know the type of pill they received. After each treatment period, patients were weighed, had blood tests, underwent psychometric testing, and indicated their therapy preference.
The researchers reported that 49% of the patients preferred desiccated thyroid extract, 19% preferred levothyroxine, and 23% had no preference. Desiccated thyroid extract use was also associated with more weight loss. There was no difference in the psychometric testing or in any symptoms. While DTE is not widely used, this study showed that many patients preferred it compared with levothyroxine. This result was observed despite there being no differences in thyroid function blood test and psychometric test results, although use of desiccated thyroid extract was associated with some weight loss. These results suggest that there may be a certain number of patients in who desiccated thyroid extract might be a reasonable treatment option.
However, a review of available literature reveals that most studies of DTE treatment are hampered by an inferior design, and data on long-term effects and side effects are lacking. Two RCTs could not demonstrate any difference in QoL or symptom scores when comparing DTE with other thyroid hormone substitutions.
Potential Benefits
Some nonrandomized studies suggest that DTE may have benefits. Symptom and QoL assessments were in favor of DTE. Some patients report feeling better on DTE, even when standard thyroid function tests show no significant difference compared to levothyroxine. The previously mentioned study also indicated that DTE use was associated with some weight loss.
Risks and Side Effects
DTE carries several potential risks and side effects:
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- Inconsistent Hormone Levels: The strength of hormones in thyroid extract is not consistent, making proper dosing difficult. Tablets made from the same manufacturing batches may not always provide the same thyroid hormone levels.
- Cardiovascular Effects: Included studies indicated that DTE may cause an increase in heart rate, lower body weight, and lower high-density lipoprotein compared with other treatment regimens, but results were conflicting.
- Adverse Reactions: As with any medication, allergic reactions are possible.
- Overdose: Severe and sometimes deadly side effects may happen with this drug if it is taken in large doses or with other drugs for weight loss.
- Other Side Effects: Hair loss may happen in some people in the first few months of using this drug.
It is very important that your doctor check the progress of you or your child at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests will be needed to check for unwanted effects.
Call your doctor right away if you start to have chest pain, fast, irregular, pounding, or racing heartbeat or pulse, excessive sweating, heat intolerance, nervousness, or any other unusual medical condition.
Precautions and Warnings
Several precautions are necessary when considering or using DTE:
- Not for Weight Loss: Thyroid should not be used for the treatment of obesity or for the purpose of losing weight. This medicine is ineffective for weight reduction and when taken in larger amount, it may cause more serious medical conditions.
- Infertility: Thyroid should not be used for the treatment of infertility unless it is caused by hypothyroidism.
- Diabetes: For patients with diabetes: It is very important that you keep track of your blood or urine sugar levels as instructed by your doctor. Check with your doctor immediately if you notice any changes in your sugar levels.
- Hair Loss: A temporary loss of hair may occur during the first few months of thyroid therapy. Ask your doctor about this if you have any concerns.
- Stopping Treatment: Do not suddenly stop taking this medicine without first checking with your doctor. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely.
- Other Medications: Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.
- Allergies: Do not use this drug if you are allergic to this drug; any part of this drug; or any other drugs, foods, or substances.
- Other Conditions: Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take this drug with all of your drugs and health problems. Tell all of your health care providers that you take this drug. If you have high blood sugar (diabetes), talk with your doctor. This drug may sometimes affect blood sugar control.
- Source Concerns: This drug is made from pork (pig) thyroid tissue. There is a very small risk of getting a viral disease from this drug. No cases have been reported.
- Older Adults: If you are 65 or older, use this drug with care.
- Pregnancy and Breastfeeding: Tell your doctor if you are pregnant, plan on getting pregnant, or are breast-feeding.
Interactions
Thyroid extract contains the thyroid hormones triiodothyronine (T3) and thyroxine (T4). Levothyroxine is used to increase thyroid hormone levels in people whose levels are too low. Be cautious with this combination. Talk with your health provider.
Dosage
The appropriate dose of thyroid extract depends on several factors such as the user's age, health, and several other conditions. At this time there is not enough scientific information to determine an appropriate range of doses for thyroid extract (in children/in adults). Keep in mind that natural products are not always necessarily safe and dosages can be important.
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FDA's Position and Actions
Professional medical society guidelines recommend synthetic levothyroxine as the preferred treatment for hypothyroidism, with the goal of normalizing thyroid hormone levels.
FDA sent letters to manufacturers, importers and distributors of marketed unapproved animal-derived thyroid medications on Aug. 6, 2025. This letter notified them of the agency’s intent to take action against unapproved animal-derived thyroid medication. Doctors will be able to work with their patients to safely transition them to an FDA-approved thyroid hormone replacement medication.
Manufacturers, importers and distributors of unapproved animal-derived thyroid medications may be subject to compliance action if they commercially distribute their unapproved products. Additionally, these unapproved animal-derived thyroid medications are not eligible for compounding because these products are regulated as biological products under the Public Health Service Act.
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. The agency urges patients taking these unapproved animal-derived thyroid medications to treat hypothyroidism to talk to their doctor. Your primary care doctor or a professional medical society, such as the Endocrine Society or the American Association of Clinical Endocrinologists, can help identify an experienced endocrinologist, which is a specialist who supports patients with thyroid and other hormone disorders.
FDA encourages health care providers to contact patients taking unapproved animal-derived thyroid medication to transition them to an FDA-approved medication to treat hypothyroidism.