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Armour Thyroid Uses & Risks

Written by Mathew Eng, PharmD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Mathew Eng, PharmD | Last updated:

Over 100 years ago, doctors started making extracts from the dried, ground-up thyroid glands of pigs to treat thyroid disorders. Uncover the unique history of Armour Thyroid and find out how it compares to modern treatments such as levothyroxine.

What Is Armour Thyroid?

Armour Thyroid is the brand name for a naturally-derived medication called desiccated thyroid extract. Other brand names include NP Thyroid and Nature-Throid. Although all of these thyroid extract medications require a prescription, they are not approved by the FDA.

These extracts are made from the thyroid glands of animals, typically from pigs. The thyroid glands are first dried and turned into a powder (“desiccated”). They are then packaged into ready-to-use products [1].

Armour Thyroid is used to treat low thyroid hormone levels, also known as hypothyroidism [1].

It contains two thyroid hormones, which are normally produced by the thyroid gland: thyroxine (T4) and triiodothyronine (T3) [2].

Once the standard treatment for hypothyroidism, the use of thyroid gland extracts today has fallen out of favor, primarily due to concerns about safety and effectiveness [2, 3].

Many different organizations, including the American Association of Clinical Endocrinologists and the European Thyroid Association, recommend against the use of thyroid extracts, including Armour Thyroid [4, 5].

How Armour Thyroid Works

The thyroid gland primarily produces two hormones, thyroxine (T4) and triiodothyronine (T3) [6].

T3 is much more active and is generally the one that affects the body. T3 plays a role in a variety of functions including metabolism, heart rate, and body heat [6].

Thyroid hormone replacement (such as Armour Thyroid) is used when people cannot produce enough thyroid hormones on their own, a condition called hypothyroidism [2].

Armour Thyroid contains T3 and T4 that is extracted from pigs. These animal thyroid hormones work similarly in humans and can help restore thyroid hormone levels [2].

History of Armour Thyroid

The first recorded use of desiccated thyroid extract was in 1891. After that, animal extracts quickly became the standard treatment for hypothyroidism [1].

Even after synthetic versions of T4 and T3 were developed, thyroid extracts remained the preferred choice for a while. These animal extracts contain more T4 than T3, and many believed that the content in the extracts better matched the levels found in humans. Some practitioners still hold this stance [1].

However, several key discoveries changed how most doctors viewed thyroid extracts [1].

One major finding was that much of the T3 found in humans is converted from T4. Scientists also found that the thyroid gland normally secretes about 14 times more T4 than T3 [1].

These findings implied that the body primarily uses T4, which is converted to T3 when needed. Researchers reasoned that using T4 alone and letting the body decide when to convert it to T3 may be safer and more effective [1].

Another issue is the inconsistent quality of thyroid extract products. Multiple studies have shown that the contents inside animal thyroid extracts can vary wildly. The quality of these thyroid extracts is also not monitored by the FDA [1, 7].

Over time, these discoveries prompted a major shift towards the use of levothyroxine, a synthetic T4 medication [1].

Fast-forward to today, almost all guidelines on hypothyroidism do not recommend the use of thyroid extracts [8, 7].

Uses of Armour Thyroid

Armour Thyroid is not approved by the FDA. The safety and effectiveness of Armour Thyroid have not been evaluated for any use.

Armour Thyroid is primarily used to treat low thyroid hormone levels (hypothyroidism). It provides animal-derived thyroid hormones (T4 and T3), which the body can use for itself [1].

Desiccated thyroid extracts, like Armour Thyroid, have been used historically to replenish thyroid hormones in humans, Despite this, very few studies have evaluated their effectiveness [1].

In a randomized crossover trial of 70 patients with hypothyroidism, thyroid extract caused modest weight loss and was preferred by more patients compared to levothyroxine.

However, an analysis of 13 clinical trials and 4 systematic reviews concluded that combination therapy with T3 and T4 is not better than levothyroxine alone [8].

Armour Thyroid vs. Levothyroxine

Levothyroxine is currently the standard treatment for hypothyroidism [8].

Levothyroxine is a synthetic version of T4, which is converted to T3 by the body. In contrast, Armour Thyroid contains T4 and T3 that are extracted from pigs [1].

Health Risks of Armour Thyroid

High Amounts of T3

Armour Thyroid contains T4 and T3 in about a 4:1 ratio [8].

However, human thyroid glands naturally secrete T4 and T3 in a 14:1 ratio [8].

This means that Armour Thyroid delivers much more T3 than what is naturally produced, which may cause several problems [8, 2].

For example, studies have found that desiccated thyroid extracts cause spikes in T3 levels that can lead to hyperthyroid symptoms [9, 8].

Product Variability

One of the main reasons thyroid extracts fell out of favor was because of inconsistent product quality [1].

In the past, studies found that some desiccated thyroid extract products contained no active thyroid hormone, while others had almost double the expected amount [10, 1].

Today, the consistency of these products has improved and they are more standardized. However, their content is still more likely to vary compared to synthetic drugs like levothyroxine [1].

Not FDA-approved

Although Thyroid extracts are regulated by the FDA, they are not actually an FDA-approved medication.

This is partly because desiccated thyroid extracts existed before the formation of the FDA, so they never went through the drug approval process [2].

Their unique status makes it difficult to perform clinical trials on Armour Thyroid, due to safety and funding issues.

As a result, studies about the safety and effectiveness of Armour Thyroid are desperately lacking.

Not Recommended in Pregnancy

Many organizations, like the American Thyroid Association and the American Association of Clinical Endocrinologists, recommend against the use of desiccated thyroid extracts in pregnancy [8].

One major issue is that the safety of thyroid extracts has never been studied in pregnancy [8].

Another reason is that T4 is essential for the development of fetal brains. Thyroid extracts, which contain lower concentrations of T4, may negatively affect development [11, 8].

Levothyroxine, in comparison, has been shown to be safe and effective during pregnancy and breastfeeding [8].

Armour Thyroid Safety

Armour Thyroid is not approved by the FDA. The safety of Armour Thyroid is unknown due to a lack of clinical research. Always take your medication as directed by your doctor.

Side Effects

The side effects of Armour Thyroid have not been evaluated by clinical trials or the FDA. If you are taking Armour Thyroid and any side effects persist or worsen, let your doctor know. This is not a complete list of possible side effects. Tell your doctor if you experience any serious side effects or notice any effects not listed here.

Based on the few studies that have looked at Armour Thyroid, side effects do not appear to differ from levothyroxine treatment [12, 13].

Some common side effects of thyroid hormone replacement include [14]:

  • Headache
  • Sleep problems
  • Tiredness
  • Changes in appetite and weight
  • Fever
  • Sweating

Some serious side effects of thyroid hormone replacement include [14]:

  • Mood or mental changes
  • Shortness of breath
  • Chest pain
  • Irregular heartbeat
  • Swelling in the hands, ankles, or feet

Often, side effects are due to imbalances in thyroid hormones and not from the medication itself. If thyroid hormone levels are within normal range, side effects are usually uncommon [8].

Because of their high T3 concentration, thyroid extracts may be more likely to cause thyrotoxicosis, or an excess of thyroid hormones [15, 8].

Some symptoms of high thyroid hormone levels include [16]:

  • Appetite changes
  • Difficulty sleeping
  • Tiredness
  • Sweating
  • Irritability


Armour Thyroid is generally not recommended during pregnancy [8].

This is mostly due to a lack of research – no studies have looked at the safety of desiccated thyroid extracts in pregnancy [8].

Another issue is that desiccated thyroid extracts contain lower concentrations of T4 compared to levothyroxine. Research suggests that adequate T4 levels are crucial for fetal brain development [11, 8].

If you are pregnant or plan to become pregnant, it’s best to discuss treatment options with your doctor.


Thyroid hormone medications should not be taken in certain situations, including [14, 17*]:

  • When thyroid hormones are elevated, such as in thyrotoxicosis
  • During a heart attack
  • With uncorrected adrenal insufficiency
  • If there is an allergic reaction to drug ingredients

*Based on manufacturer’s product label

Drug Interactions

The following drugs have been reported to interact with Armour Thyroid. However, this is not a complete list, let your doctor know of all the medications you are currently taking to avoid any unexpected interactions.

Some potential interactions include [17*]:

*Based on manufacturer’s product label

There is a case report of a male adult experiencing a heart attack after using testosterone and Armour Thyroid together. The man was using the two medications in order to lose weight and gain muscle [18].

Armour Thyroid Dosage & Strengths

The dosing of Armour Thyroid can vary. Always take this medication as directed by a doctor.

Armour Thyroid comes in tablet form with strengths that range from 15 mg to 300 mg.

Dosage strengths are sometimes written in grain, an old unit of measurement. For Armour Thyroid products, one grain is equal to 65 mg, which is sometimes listed as 60 mg [8].

Armour Thyroid contains T3 and T4 in about a 1:4 ratio.

For example, a 60 mg tablet contains about 9 mcg (micrograms) of T3 and 38 mcg of T4 [8].

A typical starting dose of Armour Thyroid for adults is a 30 mg tablet per day, but should be individualized to each person. It is adjusted by increments of 15 mg every 2 – 3 weeks, based on lab results of TSH, T3, and T4.

Maintenance doses usually range from 60 mg to 120 mg per day.

Armour Thyroid Ingredients

Aside from the crushed thyroid glands of pigs, other ingredients in Armour Thyroid are calcium stearate, dextrose, microcrystalline cellulose, sodium starch glycolate and opadry white.

These are used to manufacture the pills and give them adequate consistency and appearance.


Once the mainstay treatment for hypothyroidism, Armour Thyroid has largely been replaced with synthetic thyroid medications. Armour Thyroid has fallen out of favor due to concerns about its safety and effectiveness.

About the Author

Mathew Eng

Mathew Eng

Mathew received his PharmD from the University of Hawaii and an undergraduate degree in Biology from the University of Washington.
Mathew is a licensed pharmacist with clinical experience in oncology, infectious disease, and diabetes management. He has a passion for personalized patient care and believes that education is essential to living a healthy life. His goal is to motivate individuals to find ways to manage their chronic conditions.


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