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Can You Be Allergic To Thyroid Medication?

Learn how to distinguish between an allergy or sensitivity to your thyroid medication in this article.
Can You Be Allergic To Thyroid Medication?
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Medications usually contain other products besides the active ingredients to help them. Fillers are inactive ingredients that play an important role in ensuring the drug is consistent and reproducible. They also help your body absorb the medication more efficiently. The amount of active ingredients is often too small to be contained in a pill or capsule, so fillers also help make the drug manageable in size. But sometimes, these ingredients cause sensitivities or even allergic reactions. Here’s what you should know about having an allergy to the thyroid medication you take for hypothyroidism.

The difference between a drug allergy and sensitivity

People often use allergy and sensitivity interchangeably. But these are two very different responses that need defining.


An allergy is a reaction to something outside of your body that triggers an immune response. Usually, an allergy results from an immunoglobulin E (IgE) mediated reaction. IgE’s are antibodies that cause your body to react when exposed to an allergen immediately. This immediate immune response causes histamine to be released, which can lead to several severe symptoms, including:

  • Hives and itching
  • Airway constriction, wheezing, and shortness of breath
  • Swelling
  • Vomiting and diarrhea

This type of reaction can sometimes lead to anaphylaxis, which can be life-threatening and requires immediate medical attention.


A sensitivity is also sometimes called an intolerance. This type of response from the body is usually because your body cannot break down specific proteins in foods or additives in medicine. Typically, people develop a sensitivity if they:

  • Do not have the proper enzymes to break down particular proteins, such as the lactase enzyme necessary to break down lactose,
  • Are sensitive to caffeine and other chemicals used in pharmaceuticals, or
  • They are sensitive to sugars that are naturally in certain types of food.

The most common types of sensitivities occur with food. Not surprisingly, most of the symptoms associated with a sensitivity occur in your digestive system. These symptoms include:

  • Cramping
  • Nausea
  • Diarrhea
  • Constipation
  • Bloating


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How to tell if you have an allergy or sensitivity

“True allergies” to foods and chemical products are rare, but sensitivities are relatively common. Yet, the symptoms of either can be concerning and may lead you to seek a firm diagnosis. 

Allergy testing is one of the best ways to determine if you have an allergy or not. People can get allergy testing for various things, including foods, animals, pollens, dust, mold, and drugs. 

There are several different ways to test for allergies:

Scratch test

A scratch test is performed on your back. An allergy doctor will determine what needs to be tested based on your concerns and will apply a little serum with the allergen inside it with a small prick on your back. The prick is just light enough to alert the immune system that damage has occurred and sends immune cells to investigate and heal. If you have an allergy to the serum in that specific area, you will develop a wheal that becomes red, itchy, and inflamed. Your allergist will measure the size of the reaction to determine how allergic you are to the item in question.

Patch test

Sometimes, allergists apply a patch on your back with chemicals or ingredients you suspect may be triggering symptoms. The type of reaction detected by a patch test is a little bit different than an IgE-mediated reaction. However, it can help identify if you are sensitive to certain chemicals found in medications, cosmetics, and common household goods you are exposed to regularly (like laundry detergent).

Blood test

Allergists also can do blood tests. However, this type of testing is not often used to detect medication allergies, as the research on this testing is limited and is not always accurate. 

Can I be allergic to my thyroid medication?

Thyroid medication usually makes people with hypothyroidism feel better as it replaces the thyroid hormones they are missing. Still, sometimes people can have sensitivities to this medication and rarely allergic reactions. Sensitivities and allergic reactions are generally due to the filler used in these medications. 

The filler ingredients vary based on the brand you take. Common filler ingredients in common T4 medications include:

  • Lactose
  • Cornstarch
  • Gluten
  • Sucrose
  • Dyes
  • Acacia

In rare cases, people can have a true drug allergy to T4 medications. However, it is more likely that you can be sensitive to something in the medicine that causes symptoms like bloating, diarrhea, cramping, and headaches.

Chart of inactive ingredients in T4 thyroid medications
Chart of inactive ingredients in T3 thyroid meds

How to know if you are allergic or sensitive to your thyroid medication

Identifying a drug sensitivity can be challenging, whereas an allergy is more straightforward given the severity of the symptoms. If you suspect you cannot tolerate your thyroid medication, try to keep a daily journal of your symptoms. Track when you take all of your medications, the foods you eat, and anything else that may be relevant. 

Take your journal to your thyroid doctor and share your concerns and findings. Making a diagnosis of a drug sensitivity or allergy requires a thorough history of your symptoms, so a journal can be a valuable tool for your doctor. 

Your doctor may offer several diagnostic tools to help figure out the cause of your symptoms, including:

  • A lactulose breath test
  • An elimination diet
  • Allergy testing (patch test, or less commonly a blood test)
  • A tTG-IgA test (Tissue Transglutaminase IgA antibody) to test for celiac disease

Although switching your thyroid medication brands is usually discouraged, your doctor may try you on a different medication if you struggle with some of the ingredients in your medicine. For example, if you have a lactose sensitivity, you may need to switch to a medication like Tirosint, a levothyroxine brand free of acacia and lactose. 

Some people may also benefit from natural desiccated thyroid, which has fewer inactive ingredients.

A note from Paloma Health

Are you worried about a possible allergy or sensitivity to your thyroid medication? Chat with a trusted Paloma Health thyroid doctor to find the best thyroid treatment plan personalized for you.

Dealing with Hypothyroidism?  Video chat with a thyroid doctor

Get answers and treatments in minutes without leaving home - anytime. Consult with a U.S. board certified doctor who only treats hypothyroidism via high-quality video. Insurance accepted.


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Julia Walker, RN, BSN

Clinical Nurse

Julia Walker, RN, BSN, is a clinical nurse specializing in helping patients with thyroid disorders. She holds a Bachelor of Science in Nursing from Regis University in Denver and a Bachelor of Arts in the History of Medicine from the University of Colorado-Boulder. She believes managing chronic illnesses requires a balance of medical interventions and lifestyle adjustments. Her background includes caring for patients in women’s health, critical care, pediatrics, allergy, and immunology.

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