Armour Thyroid (desiccated thyroid) is a prescription oral tablet used to treat certain thyroid disorders in adults and children. Armour Thyroid can cause side effects that range from mild to serious. Examples include fast heart rate and sweating.

Armour Thyroid has a boxed warning, which is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Side effects explained” section.

Some people may experience mild to serious side effects during their Armour Thyroid treatment.

It’s not known how often side effects occur with Armour Thyroid or which side effects occur more commonly. The drug became available before the Food and Drug Administration (FDA) started its drug approval process. Because of this, no studies were done to find out how often side effects may occur with Armour Thyroid.

Side effects usually only occur with Armour Thyroid if the levels of thyroid hormones in your system get too high. This is called thyrotoxicosis. It can happen if you take too much Armour Thyroid (such as if your dose is too high). To learn more about this side effect, see the “Side effects explained” section.

Mild side effects have been reported with Armour Thyroid. These side effects usually only occur if the levels of thyroid hormones in your system get too high. This can happen if you take too much Armour Thyroid (such as if your dose is too high).

Examples of mild side effects that can occur with thyrotoxicosis caused by too much Armour Thyroid include:

In most cases, these side effects should be temporary and easily managed. If they occur, talk with your doctor. If you have symptoms that are ongoing or bothersome, talk with your doctor or pharmacist. And do not stop taking Armour Thyroid unless your doctor recommends it.

Armour Thyroid may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Serious side effects have been reported with Armour Thyroid. These side effects usually only occur if the levels of thyroid hormones in your system get very high. This can happen if you take too much Armour Thyroid, such as if your dose is too high.

Examples of serious side effects that can be caused by too much Armour Thyroid include:

If you develop serious side effects while taking Armour Thyroid, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see the “Side effects explained” section.

Note: The Food and Drug Administration (FDA) tracks and reviews side effects of medications. If you’d like to notify the FDA about a side effect you’ve had with Armour Thyroid, visit MedWatch.

Allergic reaction

For some people, Armour Thyroid can cause an allergic reaction.

In general, symptoms of allergic reaction can be mild or serious.

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms and can determine whether you should keep taking Armour Thyroid.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Armour Thyroid, they may have you switch to a different treatment.

Get answers to some frequently asked questions about Armour Thyroid’s side effects.

Does Armour Thyroid have any long-term side effects?

It’s not likely. Long-term side effects have not been reported with Armour Thyroid.

However, Armour Thyroid became available before the FDA started its drug approval process. Because of this, no studies were done to investigate possible long-term side effects that may occur with the drug.

Armour Thyroid typically only causes side effects if you take too much of the drug, such as if your dose is too high.

If you have questions or concerns about possible long-term side effects of Armour Thyroid, talk with your doctor.

Can Armour Thyroid cause hair loss?

It might, in some cases. For example, you may have hair loss if the levels of thyroid hormones in your system get too high. This is called thyrotoxicosis.* It can happen if you take too much Armour Thyroid, such as if your dose is too high.

If you have hair loss while taking Armour Thyroid, talk with your doctor. They may need to lower your dose of the medication. Your hair will usually grow back when your thyroid hormone levels return to normal.

Partial hair loss or thinning has also occurred in some children in the first few months of taking thyroid hormones. (Armour Thyroid contains thyroid hormones.) If a child has hair loss when taking thyroid hormones, this is usually temporary, and the hair will soon grow back.

If you have questions or concerns about hair loss with Armour Thyroid, talk with your doctor.

* To learn more about this side effect, see the “Side effects explained” section.

Does Armour Thyroid cause weight gain?

It’s not likely. Thyroid hormones don’t usually cause weight gain. (Armour Thyroid contains thyroid hormones.)

However, weight gain can be a symptom of low thyroid hormone levels, which Armour Thyroid is used to treat. Correcting low thyroid hormone levels with Armour Thyroid may lead to weight loss rather than weight gain.

If you have unexpected weight gain while taking Armour Thyroid, talk with your doctor. They can help determine the cause.

Learn more about some of the side effects Armour Thyroid may cause.

Thyrotoxicosis

You may have thyrotoxicosis (high levels of thyroid hormones in your body) when taking Armour Thyroid. However, this usually only occurs if you take too much Armour Thyroid, such as if your dose is too high. It’s not known how often this occurs.

Thyrotoxicosis may cause symptoms such as:

  • fast heart rate
  • heart palpitations
  • tremor
  • muscle weakness
  • sweating or feeling too hot
  • nervousness or anxiety
  • frequent bowel movements

What might help

If you have symptoms of thyrotoxicosis during Armour Thyroid treatment, talk with your doctor. They’ll likely reduce your dosage of Armour Thyroid.

If you have questions about your Armour Thyroid dosage and your risk of side effects, talk with your doctor.

Thyroid storm

If you have thyrotoxicosis (see above) that’s not well managed while taking Armour Thyroid, this could lead to a thyroid storm. With this condition, the levels of thyroid hormones in your body are dangerously high. Thyroid storm is a medical emergency that can be life threatening.

Thyroid storm usually only occurs if you take too much Armour Thyroid, such as if your dose is too high. It’s not known how often this side effect occurs, but it’s likely rare.

Symptoms of a thyroid storm can include:

  • racing heart rate (tachycardia) that exceeds 140 beats per minute
  • atrial fibrillation
  • high blood pressure
  • high fever (104°F to 106°F or 40°C to 41°C)
  • shaking
  • agitation or restlessness
  • confusion
  • fast breathing or shortness of breath
  • diarrhea
  • jaundice (yellowing of your skin or the whites of your eyes)

What might help

If you have symptoms of a thyroid storm while taking Armour Thyroid, call 911 or your local emergency number right away. This condition needs urgent medical treatment.

If you have questions about the risk of a thyroid storm when taking Armour Thyroid, talk with your doctor.

Serious or life threatening side effects if taken for weight loss

Armour Thyroid has a boxed warning about the risk of serious or life threatening side effects if the drug is taken for weight loss. A boxed warning is the most serious warning from the FDA.

Armour Thyroid is used to increase low thyroid hormone levels. One of the symptoms of low thyroid hormone levels is weight gain. So, correcting low thyroid hormone levels with Armour Thyroid can lead to weight loss.

However, if you have normal levels of thyroid hormones, taking Armour Thyroid for weight loss can make your thyroid hormone levels get dangerously high. This can cause serious or even life threatening side effects. Examples include:

What might help

You should not take Armour Thyroid as a weight loss aid. If you’re interested in taking medication to help with weight loss, talk with your doctor. They can recommend safe treatment options that may be right for you.

Keeping track of side effects

During your Armour Thyroid treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Armour Thyroid affects you. They can then use this information to adjust your treatment plan if needed.

Below is important information you should consider before taking Armour Thyroid.

Boxed warning: Risk of serious or life threatening side effects if taken for weight loss

Armour Thyroid has a boxed warning, which is the most serious warning from the FDA. For details, see the “Side effects explained” section.

Other warnings

Armour Thyroid can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors may also affect whether Armour Thyroid is a good treatment option for you.

Talk with your doctor about your health history before you take Armour Thyroid. Be sure to tell them if any of the following factors apply to you:

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.