Antibiotics and Thyroid Hormone Production

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Antibiotics are widely prescribed to treat bacterial infections.

Through their mechanisms of action, the antibiotics either kill the bacteria or prevent them from copying and reproducing themselves. The use of different medications can affect other processes in the body, and antibiotics aren’t the exception.

Therefore, it’s impossible not to wonder if antibiotics have any impact on thyroid hormone production.

Learn more about what happens with thyroid hormones with antibiotics use. How does the thyroid gland act when you’re taking antibiotics?

Antibiotics use overview

Most people will use antibiotics at some point in their lifetime as these drugs are widely prescribed. According to the CDC, more than five antibiotics prescriptions are written each year for every six people in the United States. An estimated 80-90% of the volume of human antibiotic use occurs in the outpatient setting[i].

The U.S. has the fourth-largest prescribing rate of antibiotics in the world. For example, in 2015, the U.S. wrote nearly 270 million antibiotic prescriptions, which amount to 838 antibiotic prescriptions for every 1000 people[ii].

On a global level, the use of antibiotics has increased by 65% over the 15-year period[iii].

As seen above, antibiotics are prescribed more often than most of us think. For that reason, it’s crucial to learn whether they affect your thyroid and, if so – how they do it.

Antibiotics impair gut

The importance of healthy get is largely underestimated. The gut microbiome helps control digestion and strengthens the immune system. Functions of gut microbiota are truly numerous and extend to brain health support, weight management, heart health, blood sugar control, among others.

Antibiotics may induce various side effects, and impaired gut health is one of them. A growing body of evidence confirms that antibiotics not only act on infection-causing bad bacteria but also the host’s microbiota. In other words, the use of antibiotics can exhibit negative effects on good bacteria necessary for optimal gut health. For example, the treatment with antibiotic ciprofloxacin in healthy subjects influenced the abundance of about one-third of bacteria. These changes can reduce the richness, diversity, and evenness of the bacteria community. The negative effects of antibiotics on gut microbiome can be short-term or long-term i.e., permanent[iv]. This is particularly concerning nowadays when antibiotics are overprescribed.

An increasing number of studies point to the detrimental impact of antibiotics on gut health. For instance, the Nature Microbiology published a research which showed that the composition and function of gut bacteria could recover after antibiotic treatment in healthy people. That being said, after six months, the gut of participants still lacked nine common beneficial bacterial species. The broad-spectrum antibiotics may dilute the diversity of the intestinal bacterial ecosystem. These results are a source of concern for doctors and scientists due to potentially permanent loss of beneficial bacteria after exposure to antibiotics. Western populations tend to have a lower diversity of gut microbiota than people in Africa or the Amazon region, and the theory is that the widespread use of antibiotics is one of the main factors[v].

Why does this story about the impact of antibiotics on gut health matter?

It matters because gut health is important for thyroid health and hormone production.

Evidence shows that the gastrointestinal tract interacts actively with T3 and T4 thyroid hormones. What many people don’t know is that the gut plays a major role as a reservoir for the hormones produced by the butterfly-shaped gland, particularly T3. Additionally, the gut may also take part in the regulation of hormone activity[vi].

Bacteria in the gut support numerous functions in the body, and the production of active thyroid hormones is one of them. About 20% of thyroid function depends on the sufficient supply of healthy gut bacteria to convert T4 to T3 hormone. The impaired gut health disrupts the production of active thyroid hormone[vii]. Numerous factors can impair gut health ranging from an unhealthy diet to antibiotics.

Imbalance of gut microbiota can decrease thyroid hormone levels, dull thyroid hormone receptor sites, elevate the levels of inactive T3, lower TSH, and promote the development of autoimmune thyroid disorders. For example, the most common cause of hypothyroidism is the autoimmune condition Hashimoto’s thyroiditis. Since about 80% of the immune system resides in the gut, then poor digestive health is a major factor in triggering and worsening autoimmune conditions such as Hashimoto’s. That’s why repairing gut health is a significant factor in the management of Hashimoto’s disease.

Gut health and thyroid health go hand in hand

Therefore, antibiotics can impair gut health and balance of good and bad bacteria. Impaired gut health has a negative impact on thyroid hormone levels and their production.

Antibiotics affect zinc effectiveness

Zinc is a mineral with a wide spectrum of functions in the body. This micronutrient is required for growth and development, gene expression, wound healing, DNA synthesis, immune function, protein synthesis, and more. The second most abundant trace mineral in the body also plays a role in the production of testosterone, skin health, and it is present in every cell. The importance of zinc is truly immense, and it also extends to thyroid function. Without this mineral, the butterfly-shaped gland and its hormones wouldn’t work properly.

You see, when zinc levels are low, then TSH is not produced. In turn, the levels of T3 and T4 hormones decrease[viii]. Zinc also happens to be a vital part of enzyme deiodinase, which converts T4 into T3. Therefore, decreased concentration of zinc disrupts the production and conversion of thyroid hormones and could contribute to problems such as hypothyroidism. A great example is a case study where zinc deficiency has contributed significantly to the development of hypothyroidism. Symptoms such as depression, appetite problems, taste acuity, hair loss, and skin lesions showed major improvement with zinc supplementation[ix].

As shown above, zinc is crucial for thyroid health and the production of thyroid hormones. But, antibiotics can reduce the effectiveness of zinc and thereby impair its influence on thyroid. Moreover, zinc is also necessary for a strong immune system. Reduced effectiveness of zinc due to antibiotics can also weaken the immune system defenses and potentially contribute to autoimmune conditions.

In other words, some antibiotics can harm thyroid hormone productions by dampening the effectiveness of zinc, much-needed mineral for the proper function of this gland and its hormones.

Since you’re probably wondering how to determine whether you have low zinc levels, you can see the most common signs and symptoms below:

  • Open sores on the skin
  • Delayed wound healing
  • Unexplained weight loss
  • Diarrhea
  • Loss of appetite
  • Lack of alertness
  • Reduced sense of smell and taste

Antibiotics can affect thyroid function in kids and adolescents.

When we’re discussing thyroid function, we usually talk about adults and the role of different factors on the health of their butterfly-shaped gland. But the truth is that children and adolescents can also experience problems, but they’re largely overlooked.

Studies show that antibiotics minocycline and doxycycline can lead to more severe thyroid dysfunction in children and adolescents than previously thought. Thyroid-related problems caused by these antibiotics appear to be non-autoimmune chemical thyroiditis leading to cytotoxic damage sufficient to cause marked release of thyroid hormones and even permanent hypothyroidism in some cases[x].

Taking thyroid medications and antibiotics

If you’re taking thyroid medications such as levothyroxine, now you are probably wondering whether it’s safe to take antibiotics or how to recover from bacterial infections for which these drugs are usually prescribed.

Studies show that antibiotic ciprofloxacin can decrease the absorption of levothyroxine[xi], the hormone replacement prescribed to patients with hypothyroidism. Therefore, using this antibiotic with thyroid medication could decrease the effectiveness of the latter and thereby impair the management of underactive thyroid.

What to do then?

Well, the first and most important thing is to inform the doctor about medications you’re taking (if you’re seeing a different healthcare provider). Your doctor will inform you whether it’s safe to take the antibiotic with thyroid medications and advise you on how to do so without experiencing side effects, low thyroid hormone levels, and other problems.

It’s important to adhere to a doctor’s recommendations and guidelines. That’s the best way to remain healthy and support thyroid health at the same time.

The impact of antibiotics on the absorption of thyroid medications could be minimized if these two drugs are taken six hours apart. But this is still a subject of many debates among scientists and physicians. The important thing is that you shouldn’t alter dosages or the time when you take them without consulting your doctor.

Side effects of antibiotics

Negative reactions to antibiotics aren’t uncommon. For instance, figures show that one in 15 people experience an allergic reaction to antibiotic medications. Side effects are also common, affecting one in 10 patients[xii], and although people may experience them differently, the most common adverse reactions are:

  • Loss of appetite
  • Nausea
  • Vomiting
  • Diarrhea
  • Bloating and indigestion
  • Abdominal pain

The above-mentioned side effects are usually mild and tend to go away once the course of treatment is finished. That being said, some patients may experience more severe adverse reactions which include:

  • Severe diarrhea
  • Blood in stool
  • Uncontrollable vomiting
  • Fever
  • Intense stomach pain and cramping

Even though they are designed to kill bad bacteria, sometimes the antibiotics can do the opposite and destroy good bacteria as well. That’s why many people who take antibiotics develop fungal infections in their mouth, throat, or vagina.

Some antibiotics can also induce photosensitivity and stain your teeth.

How to lower the risk of antibiotics side effects

Even though antibiotics can be pretty powerful and able to destroy bad bacteria that make you sick, these drugs can have a negative impact on our health. As mentioned above, they can harm the thyroid, induce various side effects, and impair gut health. But it’s possible to lower the risk of these adverse reactions. Below you can see a few useful suggestions:

  • Take antibiotics exactly as directed – although this seems like a no-brainer, many people tend to adjust dosages and intake of antibiotics as they see fit. Listen to doctor’s orders, especially if you’re also taking thyroid medications.
  • Finish the course of treatment – a common mistake that people make is that they stop taking antibiotics as soon as they feel better. This increases the risk of re-infection, after which you may need to take antibiotics again, all of which can harm your gut and thyroid.
  • Avoid alcohol – both alcohol and antibiotic medications may induce similar side effects, which worsen when you take them together.
  • Take probiotics – one way to protect gut health when taking antibiotics is to get probiotics i.e., healthy bacteria, which will promote the balance of gut microbiota. Always keep in mind that a healthy gut equals a healthy thyroid gland.
  • Consult your doctor – don’t be afraid to talk to your doctor, express your concerns, and ask whether it’s possible to take alternatives that could do the same job but without a negative impact on your thyroid.


Antibiotics are among the most frequently prescribed medications in the world.

Despite their potential to help us beat bacterial infections, antibiotics can also harm us.

They can disrupt thyroid function and hormone production through several mechanisms, including poor gut health and lower zinc effectiveness.

That being said, the impact of antibiotics on thyroid requires further research to understand all the underlying mechanisms associated with it.


[i], Measuring patient antibiotic prescribing, CDC. Retrieved from:[ii] Trends in U.S. antibiotic use, 2018, PEW. Retrieved from:

[iii]. Global antibiotic use has increased – sparking fears of worldwide resistance, NHS. Retrieved from:

[iv] Antibiotics alter the gut microbiome and host health, Nature Research. Retrieved from:

[v] Pedersen O, Palleja A, Mikkelsen SK, et al. Recovery of gut microbiota of healthy adults following antibiotic exposure. Nature Microbiology 2018 Oct;3(11):1255-1265.

[vi] Hays MT. Thyroid hormone and the gut. Endocrine Research, 1988;14(2-3):203-24.

[vii]. Good thyroid health depends on good gut health, Dr. K. News. Retrieved from:

[viii] Ertek S, Cicero AF, Caglar O, Erdogan G. Relationship between serum zinc levels, thyroid hormones, and thyroid volume following successful iodine supplementation. Hormones, 2010 Jul-Sep;9(3):263-8.

[ix] Betsy A, Binitha M, Sarita S. Zinc deficiency associated with hypothyroidism: an overlooked cause of severe alopecia. International Journal of Trichology. 2013;5(1):40–42.

[x] Pollock AJ, Seibert T, Allen DB. Severe and Persistent Thyroid Dysfunction Associated with Tetracycline-Antibiotic Treatment in Youth. J Pediatr. 2016;173:232–234.

[xi] Cooper JG, Harboe K, Frost SK, Skadberg Ø. Ciprofloxacin interacts with thyroid replacement therapy. BMJ. 2005;330(7498):1002.

[xii] Antibiotics side effects, NHS. Retrieved from:

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