Don’t Take These Drugs Without Knowing How They May Affect Your Thyroid

Thyroid drug interactions

Several commonly used drugs can affect thyroid function and interact with thyroid medication. In fact, they are commonly encountered in medical practice because levothyroxine is widely prescribed as are many other of the interacting drugs.

If you are taking any type of thyroid medication you must be aware of these interactions and prevent any side effects from occurring.

4 Ways How Drug Interactions Can Affect Your Thyroid

1. Some drugs can trigger a thyroid disease

Antibiotics are probably the most often used drug with largely underestimated connection to the thyroid gland. In fact, research studies confirmed that frequent use and overuse of antibiotics can actually trigger autoimmune Hashimoto’s disease and anti-thyroid side effects.

While antibiotics discovery was one of the biggest breakthroughs in fighting infections and saving many lives it came with a huge side effect that was discovered many years later. Antibiotics have the ability to damage the intestinal gut barrier and trigger autoimmune disease by promoting leaky gut.

Antibiotics kill not only bad but also all good bacteria creating an imbalance that favours overgrowth of pathogenic bacteria or intestinal dysbiosis. These pathogenic bacteria produce endotoxins called lipopolysaccharide or shortly LPS that damage the intestinal tight junctions, destroy the gut barrier, make it leaky and set the stage for an autoimmune disease

Based on the work of Prof. Alessio Fasano leaky gut is one of necessary 3 factors needed for a person to develop an autoimmune disease. You can read about it here

Interferons are currently the major treatment approach for several malignant and non-malignant diseases such as chronic hepatitis C and B, multiple sclerosis, hematological malignancies, malignant melanoma and renal cell carcinoma. Both autoimmune and non-autoimmune thyroid disorders develop in some of the interferon treated patients with the incidence ranging from 1% to 35%.

Immunomodulating drugs used for a long time such as interferon-α and interleukin-2 are known to induce variably high incidence of autoimmune thyroid disease. For example, interferon alpha (IFNα) is used for treatment of chronic hepatitis C. As a result up to 10% of patients develop clinical thyroiditis and up to 30% develop subclinical Hashimoto’s disease.

A new generation of immune checkpoint inhibitors such as anti-CTLA4 monoclonal antibodies can trigger thyroiditis and induce secondary hypothyroidism by affecting the pituitary gland. Central hypothyroidism is a well-known side effect of bexarotene which is used for the treatment of lymphoma as well as off label for lung and breast cancer.

2. A number of drugs can block thyroid function, hormones production and conversion, increase thyroid antibodies and make you hypothyroid.

Amiodarone is an iodine containing drug, which is prescribed to patients to treat arrhythmia (irregular heart beat). A greater frequency of increased thyroid peroxidase antibodies (TPO Ab) was found in female patients using amiodarone especially when the treatment lasted longer than 24 months.

Chronic administration of the drug may lead to disturbances in thyroid hormone metabolism and thyroid dysfunction. Amiodarone inhibits peripheral T4 to T3 conversion that results in increase of serum free T4, reverse T3 and TSH concentrations and a decreased serum level of free T3. Amiodarone may induce thyrotoxicosis or hypothyroidism in individuals with normal or increased iodine levels and/or pre-existing thyroid disease.

Lithium is a common treatment for bipolar disorder, which is also called manic depression. The drug inhibits release of the thyroid hormones contributing to the development of hypothyroidism, goiter and changes in the texture of the gland detectable by ultrasound.

Lithium may also cause chronic autoimmune thyroiditis with hypothyroidism in 20 to 40% of patients. Up to 50% of lithium-treated patients may develop a lithium-induced goiter after 2 years of therapy. Use of lithium in combination with pharmacological doses of potassium iodide may also result in hypothyroidism.

3. Drugs can interfere with absorption of thyroid medication making you even more hypothyroid.

Unfortunately, antibiotics use has more unwanted side effects than previously thought.

Different types of antibiotics can affect absorption of thyroid drugs. For example, an antibiotic from the quinolone family such as ciprofloxacin (brand names Cipro, Proquin, Ciproxin, Ciprobay, Cirpoxine, and Ciflox) have the ability to significantly decrease the absorption of thyroid medications, while the antibiotic rifampin or rifampicin (brand names Rifadin, Rifamate and Rifater) can significantly increase the absorption of thyroid medications.

Antacids that are often used to treat heartburn, may have absorption-inhibiting effects on thyroid medications and have to be taken 4 to 6 hours apart in order to avoid this effect.

Sucralfate used to treat ulcers and other gastrointestinal conditions inhibits the absorption of of thyroid drugs. Research shows that when the thyroid drug was given eight hours after the sucralfate this interaction could be avoided.

4. Thyroid drugs can interfere with other medications reducing its effectiveness, changing mechanism of action or causing side effects.

There are 577 drugs that are known to interact with Synthroid (levothyroxine) and 564 drugs to interact with desiccated thyroid. You can see the complete list of medications known to interact with thyroid medications here

When you think that you are safe and not at risk, think again. Many commonly used drugs are on this list:

  • Adult cold, flu and sore throat drugs like 12 Hour Cold, Alka-Seltzer, Advil and many others
  • Many allergy and congestion relief medications
  • Sinus relief drugs
  • Pain medication like acetaminophen, ibuprofen and aspirin
  • Metformin (blood sugar management drug)
  • Semvastatin (cholesterol lowering medication)
  • Contraceptives like MinOvral
  • Most weight loss and metabolism boosters especially those that contain ma huang, ephedrine and pseudoephedrine
    ….and many more.

As you can see many of these drugs don’t require a prescription and can be bought over-the-counter (OTC).

How To Protect Your Thyroid From Drug Interactions

1. Be aware about drug interactions between your thyroid medication and other drugs you take

2. Make an inventory of your medical cabinet. Write a list of all your medications including over-the-counter (OTC) drugs you are taking and ask your pharmacist to check for possible drug interactions. Pharmacies will gladly do it for you.

3. Make it as a habit to consult with your pharmacist about possible drug interactions whenever you get a new prescription or buy OTC medication.

4. If you were using antibiotics in the past and already have autoimmune Hashimoto’s there is a high probability that you have increased intestinal permeability or leaky gut syndrome. Learn about the consequences and consider gut repair as soon as possible. This alone can help you to improve many symptoms, stop and for some people even reverse autoimmune thyroid disease.

5. Consider safe alternatives when ever possible. There are effective natural antibiotics, cold and sinus remedies available that don’t cause nasty side effects and thyroid suppression.

Check out the book Everyday Roots that teaches how to replace toxic products and medications in your home with over 215 healthier, all-natural alternatives.

This is the most specific, tailored book that really narrows in on resources that are ideal for those who want to use herbs, natural remedies and essential oils safely and effectively for themselves and their family. For anyone wanting to take charge of their own health, it’s the perfect way affordably to add resources to your natural remedies library.

I am sure your thyroid will love and appreciate more natural care! To find out more about Everyday Roots book click here

P.S. Do you like what you read and want to get more? Get FREE eCourse Hypothyroidism Diet Guide

Thyroid Hormone Pathways


1. Amiodaron treatment and thyroid autoimmunity markers. Hell J Nucl Med. 2008 May-Aug;11(2):105-9.

2. Ciprofloxacin and Rifampin Have Opposite Effects on Levothyroxine Absorption. Thyroid, October 16, 2013

3. Cases of interferon-alpha and interferon-beta-induced thyroiditis. Folia Med (Plovdiv). 2010 Jul-Sep;52(3):5-12.

4. Thyroid dysfunction as an unintended side effect of anticancer drugs.Thyroid. 2013 Nov;23(11):1345-66.

5. Hashimoto Thyroiditis. S.L. Lee, S. Odeke, S.B. Nagelberg, eMedicine online publication, Mar., 2010


About Marina Gutner, PhD

Marina Gutner, PhD, researcher, medical writer, thyroid blogger, founder and Admin of Outsmart Disease who writes about life-changing treatments for hypothyroidism, Hashimoto's thyroiditis and autoimmune disease and how to balance hormones in women