Synthroid Can Cause Allergic Reactions and Sensitivity

Synthroid Could Affect Those With Hay Fever and Lactose Intolerance

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We don't always think about the possibility that the medications we take may actually make us feel worse, but it's actually more common for those of you who have allergies and sensitivities. For thyroid patients who are taking Synthroid, two ingredients in the pills are common allergens that may be causing a variety of unwanted symptoms.

Acacia in Synthroid

One of the ingredients of Synthroid brand levothyroxine is acacia. Acacia is a family of shrubs and trees, and it is used as an ingredient in some medications to provide form and shape to tablets. Some people who have pollen allergies and hay fever—especially to tree and grass pollens—may also have an allergy to acacia, even when it's an ingredient in a medication. So, for some thyroid patients with allergies, taking Synthroid can cause allergic symptoms, including mood changes, runny nose, watery eyes, and congestion, among other symptoms.

Interestingly, it also appears that people who have seasonal allergies may find that they don't respond well to their Synthroid during allergy season. One reader wrote:

"I have been taking Synthroid for 30 years and [I was] unable to find a doctor who would believe that it was making me sicker. My TSH numbers bounced from .01 to 98, and they would all say it was because I was not taking my medication correctly. I found out that Synthroid contains acacia. My high TSH spikes were during allergy season, and the low TSH was during months my allergies were not bothering me. I had chronic sinusitis and felt horrible most of the time! I now have been changed to Levoyxl and am feeling great. My sinus inflammation has gone down for the first time in at least 5 years and my lungs are clearing out."

Lactose in Synthroid

Another ingredient in Synthroid is lactose, which can trigger symptoms in people with lactose intolerance. Lactose intolerance is an inability to digest lactose, the major sugar found in milk. Lactose is also an ingredient in some foods and medications. Signs of lactose intolerance include:

  • Nausea
  • Cramps
  • Bloating
  • Gas
  • Diarrhea

Usually, the symptoms will begin 30 minutes to 2 hours after taking your Synthroid pill. (Find out more about lactose intolerance.)

Other Fillers

In addition to acacia and lactose, one of the more common fillers used in Synthroid is confectioner’s sugar, which contains cornstarch. Some studies have shown that corn proteins cross-react with gluten, which could trigger an immune system reaction to the fillers in the same way that it does to gluten. 

What Should You Do?

If you suspect you are sensitive to acacia, lactose or possible gluten trigger in Synthroid, what can you do?

First, talk to your doctor about switching to another brand of levothyroxine. If you and your doctor decide it is best for you to remain on levothyroxine, Levoxyl and Tirosint brands are both free of acacia and lactose.

You may also want to consider a natural desiccated thyroid drug, like hypoallergenic natural thyroid drug Nature-thyroid, which does not contain lactose or acacia.

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  • National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Fact Sheet on Lactose Intolerance.