How Does Caffeine Affect The Thyroid Gland

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Caffeine is a natural alkaloid chemical that many people depend on to get their day started. A recent study1 found that approximately 85% of Americans drink at least one caffeinated beverage each day. The most popular beverage that contains caffeine would be coffee, but certain sodas, energy drinks, and even tea also contain caffeine.

Caffeine consumed in small amounts can help to elevate mental performance. People find that a cup of coffee in the morning helps them wake up, while some coffee at night can help them get through a late night at work. When too much caffeine is consumed, however, risks of hypertension and adverse cardiovascular events increases. High caffeine intake is also linked to insomnia and may even interfere with the hormone production in postmenopausal women2.

One area of concern that is often overlooked is the effect of caffeine on the Thyroid Gland, as well as medications used to treat commonly diagnosed Thyroid disorders. In this post, we’ll take a closer look at whether caffeine may have an adverse impact on Thyroid health and how caffeine consumption can be controlled.

Caffeine And The Thyroid Gland

The Thyroid gland secretes three different hormones into the bloodstream. Two of the most important hormones secreted by this gland include Thyroxine and Triiodothyronine – also called T4 and T3. These hormones play vital roles in metabolic processes within the human body, and also contributes to the overall development of the body.

Limited intake of coffee should not cause excessive harm to the Thyroid gland in particular. What we want to focus on here is a higher intake of caffeine, in the form of coffee, tea, or any other caffeinated beverage.

To truly understand how caffeine affects the Thyroid gland, we have to turn our focus to the Adrenal glands for a moment. There are two Adrenal glands in the human body, and they sit atop the kidneys. Both the Adrenal glands and the Thyroid gland secrete hormones that play important roles in metabolic functions.

When a person consumes caffeine, be it from a cup of coffee or tea, or even a can of caffeinated soda, their Adrenal glands will release a series of hormones – this is essentially what causes the person to experience the boost in mental and physical energy, and what makes them more alert. The reason why the Adrenal glands release these hormones is that caffeine is known as a stimulant.

Drinking a cup of coffee now-and-then won’t cause any serious problems, but when the Adrenal glands are constantly stimulated, it can cause their function to become impaired. The hormones that are frequently released by the Adrenal glands can also start to have an adverse impact on different areas of the body – and this includes the Thyroid gland.

Caffeine consumption is linked to the secretion of adrenaline, norepinephrine, and epinephrine. These are all hormones that cause the series of effects experienced when a person drinks a cup of coffee to help them wake up in the morning and get their day started. A less documented hormone that the Adrenal glands also secretes with excessive caffeine consumption is cortisol – the “stress hormone.” One study3 asked a group of 96 participants who were asked to abstain from the use of caffeine for five days. Following the five-day period, caffeine was introduced to the bodies of the participants. The study found that cortisol levels spiked significantly following the administration of caffeine.

This is where the connection comes in and where caffeine starts to become a problem for the Thyroid gland. While adrenaline and some of the other hormones secreted by the Adrenal glands may not directly have an effect on the Thyroid, cortisol has been linked to adverse effects in relation to Thyroid function.

Doctor Amy Myers, MD, explains that there are different ways in which cortisol causes a dysfunction of the Thyroid gland4. First, when cortisol is secreted into the bloodstream, it travels to the hypothalamus and, in turn, the pituitary gland will start to reduce its secretion of hormones that trigger the Thyroid to produce both thyroxine and triiodothyronine. This already reduces the presence of Thyroid hormones in the human body, causing a decrease in metabolic function.

In addition to having a direct impact on the production of vital Thyroid hormones, cortisol can also have an adverse effect on specific enzymes that are involved in the process of Thyroid hormone conversion. Thyroxine is the more prevalent type of Thyroid hormone in the body, but it is not the “active” type of hormone produced by the Thyroid gland. A much less significant number of triiodothyronine hormones are produced by this gland, but this is the particularly important hormone that helps to regulate metabolic functions in the body – as well as contribute to many other important bodily functions.

Certain enzymes in the human body convert thyroxine into triiodothyronine hormones. There are, however, two forms of triiodothyronine, or T3 – this includes Free T3 and Reverse T3, or FT3 and RT3. When too much thyroxine is converted into RT3, then the body will slow down the conversion of these hormones. This also causes a significant slowing of metabolic functions and may also have an adverse impact on the Thyroid itself, often causing a person to experience symptoms associated with hypothyroidism. Cortisol can lead to this chain of reactions in the human body as well.

Caffeine And Levothyroxine Medication

Apart from looking at how caffeine intake can have an impact on Thyroid function, as well as Thyroid hormone conversion, there is another important topic that we need to focus on. It is well-understood in the medical industry that many things can interfere with the body’s ability to absorb levothyroxine medication adequately. This type of medication is used to treat hypothyroidism, a condition where the levels of Thyroid hormones in a patient’s body is below what is considered healthy or normal. Levothyroxine is a type of thyroxine hormone that is prepared in a laboratory. Even though other drugs have been developed for the treatment of hypothyroidism, this particular option still remains the most commonly prescribed of them all.

A study by the American Thyroid Association5 was initiated after physicians noticed the reduced effectiveness of levothyroxine medication among patients who reported taking the drug with coffee, or having a cup of coffee soon after they take the drug. The study focused on observing how coffee affected the gastrointestinal tract’s ability to absorb the levothyroxine into the body.

Even though small, the study did provide significant evidence that an interference most certainly exists between coffee or espresso consumption, and the use of levothyroxine among patients with hypothyroidism.

During the study, eight participants were divided into several groups. Each group was provided specific instructions in order to observe changes in the absorption of this particular medication. One group were provided a levothyroxine tablet with water, while others were asked to take their medication with espresso alone, espresso and water, or to take their tablet with water and have some espresso one hour afterward.

The absorption of levothyroxine into the body was reduced by 25% to 57% in the participants who took the drug with espresso. Furthermore, it was also found that espresso may delay the absorption of the drug by up to 90 minutes. Even when coffee or espresso was consumed within one hour following the administration of levothyroxine, the absorption of the drug was impaired.

According to the results of the study, patients taking levothyroxine medication to assist in the treatment of hypothyroidism, regardless of the cause, should be wary of drinking coffee with their tablets. Not only does the study prove that taking the drug with a coffee can alter the absorption, but it also proves that coffee should be avoided for at least one hour after levothyroxine medication has been taken.

Limiting Daily Caffeine Intake

Caffeine has been classified as a drug that stimulates the central nervous system and, in turn, causes a person to develop a dependence on the substance. What this means is that limiting or especially eliminating caffeine can be a difficult move to make, and may cause a person to experience certain withdrawal symptoms.

One scientific paper6 explains that while some people may only experience mild withdrawal symptoms, severe levels of distress have been reported as withdrawal from caffeine in a few patients.

Common signs of withdrawal from caffeine may include:

  • A reduction in the patient’s alertness
  • Fatigue
  • Headaches
  • Reduced energy
  • Drowsiness
  • Concentration difficulties
  • A “foggy” feeling
  • A depressed mood
  • Irritability

Approximately 50% of people will experience a headache, while as much as 13% will experience symptoms that may impair their ability to continue with their day-to-day functions.

These withdrawal symptoms tend to develop within the first 24 hours after the patient has had their last cup of coffee. They are most severe between 20 and 51 hours and may continue to be present in the patient for up to nine days in total.

Even when caffeine consumption is not excessive, giving up caffeine suddenly will most likely cause side-effects to develop.

Fortunately, for those who fear the possible withdrawal symptoms they may experience, simply limiting the intake of caffeine may produce positive results in their body, and also help to reduce the constant spike in cortisol produced by their Adrenal glands. When caffeine consumption is not completely eliminated, it is important to avoid drinking coffee too close to the administration of drugs that contain the active ingredient levothyroxine.

Individuals who want to eliminate caffeine from their diet completely should gradually reduce their dosage. This will help their body slowly reduce its dependency on caffeine and may help to reduce their risk of developing more severe withdrawal symptoms once they decide to stop using caffeine completely.


The Thyroid gland plays several important roles in the human body, making it essential for patients to realize how their diet can alter the function of this gland. High caffeine intake from coffee, tea, energy drinks, or caffeinated sodas, may spark a reaction in the body that causes impairment in Thyroid function. Not only can the Thyroid gland directly be affected by the release of cortisol, caused by excessive caffeine intake, but the conversion of Thyroid hormones can also be adversely affected. Additionally, patients already on levothyroxine for an underactive Thyroid should be wary of drinking coffee with or soon after they take their medication.


1 Multiple Authors. Beverage caffeine intakes in the U.S. Journal of Food and Chemical Toxicology. January 2014.

2 M.S. Butt, M.T. Sultan. Coffee and its consumption: benefits and risks. Critical Reviews in Food Science and Nutrition. April 2011.

3 Multiple Authors. Caffeine Stimulation of Cortisol Secretion Across the Waking Hours in Relation to Caffeine Intake Levels. HHS Public Access. 27 February 2008.

4 Dr. A. Myers. The Adrenal-Thyroid Connection. Amy Myers, MD.

5 Multiple Authors. Altered Intestinal Absorption of L-Thyroxine Caused by Coffee. Clinical Thyroidology for the Public – American Thyroid Association. March 2008.

6 K.R. Sajadi-Ernazarova, R.J. Hamilton. Caffeine, Withdrawal. StatsPearls. 11 May 2017.

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