How To Treat An Allergy to Levothyroxine

person in white shirt drinking water and taking Synthroid

Synthroid tablets (or levothyroxine sodium) are a common therapy for people living with hypothyroidism, helping combat symptoms and improve a patient’s quality of life.

Unfortunately, in rare cases, some people may experience an allergic reaction or sensitivity in response to one or more of the tablets’ inactive ingredients, which are added to help your body absorb the thyroid medication.

Throughout this post, we’re going to explore everything you need to know about:

  • How levothyroxine therapy works 
  • The risks associated with taking Synthroid and the most common allergic symptoms 
  • How best to treat and soothe an allergic reaction to levothyroxine

If you suspect your thyroid medication might be causing adverse effects, keep reading to help you identify your symptoms and treat your allergic reactions today.

How Does Levothyroxine Work?

Hypothyroidism (underactive thyroid) occurs when the body’s thyroid gland doesn’t produce enough vital thyroid hormones to regulate many of your body’s critical systems, including metabolism.

While symptoms may be undetectable at first, overtime hypothyroidism can impact you in a range of troublesome ways, causing:

  • Brain fog and mental health difficulties such as mood swings or depression
  • Increased appetite 
  • Weight gain
  • Thinning hair and hair loss
  • High blood pressure
  • Infertility
  • Cardiovascular diseases
  • Bloating
  • Muscle weakness
  • Constipation
  • Dry Skin

Levothyroxine Therapy to Treat Hypothyroidism

Taking Synthroid is one of the most popular ways of managing and mitigating the negative impacts of hypothyroidism. That’s because synthroid tablets contain a synthetic form of the T4 thyroid hormone, helping to boost your body’s hormone reserves.

To help ensure the tablets are swiftly reproduced during manufacturing and easily digested upon consumption, medicine producers will add inactive ‘filler’ ingredients to help bulk out the pill.

These inactive ingredients often contain food substances such as lactose, cornstarch, gluten, sucrose, dyes, and acacia.

Allergic Reactions to Levothyroxine

In extremely rare circumstances, some patients may be allergic to the active ingredient of the T4 thyroid replacement.

More often than not, however, allergic reactions tend to be triggered in response to the inactive ingredients added to levothyroxine tablets, particularly for people already living with specific food allergies, eczema, or asthma.

How Does An Allergic Reaction Work?

Typically, an allergy will result from an immunoglobulin E (IgE) mediated reaction.

IgEs are antibodies that detect exposure to allergens and communicate with the immune system to release histamine and other defensive chemicals to ‘protect’ your body against threatening substances (such as food allergens).

It is this immune response that is responsible for your allergic reaction symptoms.


The allergic symptoms triggered in response to levothyroxine therapy can be very diverse. Some of the most common side effects include:

  • Irritated skin, including an itchy skin rash and hives
  • Digestive issues including abdominal painnauseabloating, and diarrhea, including possible weight loss 
  • runny nose, sneezing, and wheezing
  • Heart problems
  • Difficulty controlling blood sugar levels for people with diabetes
  • In the case of a severe allergic reaction, you may experience life-threatening symptoms, including shortness of breath and chest pain. In such cases, immediate medical attention is required.

Talking To A Doctor

If you or your loved one experiences any of the above symptoms, we encourage you to consult your healthcare professional for expert advice on allergy testing.

How Are Diagnoses Made?

If you suspect that you have a possible allergy to one of the active or inactive ingredients within your levothyroxine therapy tablets, your doctor might invite you to keep a diary detailing exactly when you’re taking Synthroid, which dose you’re consuming, as well as a record of all other foods you’re eating day-to-day.

Allergies are often diagnosed through a combination of blood tests and patch tests to help identify which allergens are at the root of your problems.

Treatment for An Allergy To Levothyroxine

Managing a drug allergy is two-fold – first, there’s the task of treating the symptoms of your allergies, and second, the task of preventing another allergic attack in the first place.

How To Soothe An Allergic Skin Rash

If your levothyroxine therapy has caused you to break out in an itchy rash or a flare of hives, don’t fret! We’ve got some tips to help you soothe your aggrevated skin.

Apply A Soothing Moisturizer

The Hot Skin Soother is an excellent choice of moisturizer if you’re looking to calm even the most angry allergic skin rash.

This nourishing balm is made with organic sunflower oil and beeswax and relieves irritation in skin folds, armpits, groin areas, and elbow and knee creases.

Wear Hypoallergenic Clothing

To avoid triggering your allergic reactions, we recommend giving your skin a break by wearing soft, breathable clothing made from hypoallergenic materials.

Suppose your itchy skin rash keeps you awake at night. Why not try the 100% Organic Cotton Adult Pajamas Pants for Eczema and 100% Organic Cotton Closed Eczema Mittens for Adults to help you break the infamous itch-scratch cycle? The mid-weight cotton protects your skin from being too hot, while the soft, flat seams inside and out are perfect for sensitive, sore, or irritated skin.

Try Wet Wrapping for Intensive Relief

Wet wrapping is a traditional treatment for irritated skin that involves wrapping wet dressings around your skin’s affected area to rehydrate and soothe it.

Wet Wrapping: Step By Step

For the best results, generously moisturize your skin with a hydrating emollient such as the Organic Manuka Skin Soothing Cream.

Next, wrap your skin rash with a dampened fabric. The Remedywear™ Eczema and Psoriasis Sleeves (Bandages) are great for this step as they’re made of soothing, soft TENCEL and anti-microbial and anti-bacterial zinc oxide fibers.

Finally, cover this wet layer in a second dry layer, such as your pajamas, and sleep with your skin wet-wrapped overnight for intensive relief.

Preventing A Levothyroxine Allergy

Aside from treating your pre-existing allergy symptoms, if levothyroxine therapy is causing you trouble, it’s also essential to address the root of the problem to prevent further allergic flares.

Oral Desensitization

Oral desensitization is a treatment that involves giving a person very small but gradually increasing amounts of a substance that they are allergic to, starting with a low dose.

In the case of levothyroxine, successful oral desensitization may enable a person to continue to treat their hypothyroidism without adverse side effects.

Switching Medication 

In some cases, if oral desensitization is not possible, your doctor might invite you to change your thyroid hormone replacements and try out a new drug. 

Switching medications is a delicate process, however, and may cause the body to react unpredictably. Due to this, don’t stop taking Synthroid medicines without a doctor’s supervision. 

Manage Allergic Reactions to Levothyroxine Today

Follow these tips to help you better understand whether your replacement thyroid hormones could be taking a toll on your overall health, allowing you to manage hypersensitivity reactions and combat your allergic symptoms.


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