An overactive thyroid or hyperthyroidism does not typically lead to constipation. This condition may have the opposite effect and cause loose stool and diarrhea.

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The thyroid can produce too much or too little hormones. When it produces excess hormones, it can lead to digestive problems such as diarrhea and loose stool. Doctors call this condition hyperthyroidism.

However, if the body produces insufficient hormones, this can lead to slowed metabolism and difficulty passing stool. Doctors call this condition hypothyroidism.

This article briefly reviews what hyperthyroidism and constipation are, how thyroid issues may cause constipation, and possible treatment options.

Hyperthyroidism occurs when the thyroid produces too many hormones, such as triiodothyronine (T3) and thyroxine (T4). It affects about 1 out of every 100 Americans aged 12 years and over.

The thyroid provides hormones for various functions throughout the body. Some areas it affects include:

  • metabolism
  • nail growth
  • weight
  • energy levels
  • skin
  • internal temperature
  • hair

Hyperthyroidism may increase bowel movements, resulting in diarrhea. It may also cause several other possible symptoms, including:

Symptoms can often mimic those of other conditions. A doctor will typically require blood and imaging tests to confirm the diagnosis of thyroid issues.

Several factors can increase a person’s likelihood of developing hyperthyroidism. They include:

Constipation is a condition that affects a person’s ability to pass stool. It can cause:

  • fewer than three bowel movements a week
  • hard, lumpy, or dry stool
  • painful, difficult-to-pass stool
  • feeling like not all stool has passed

Additionally, it can cause a person to experience the following:

Hyperthyroidism typically speeds up the body’s processes. This can lead to:

  • a faster heartbeat
  • a faster metabolism, which may result in weight loss
  • looser bowel movements

Hyperthyroidism tends to cause more frequent bowel movements rather than slowing them or making them more difficult.

However, hypothyroidism, or underactive thyroid, can lead to digestive issues, such as constipation.

In an older study from 2009, researchers noted that hypothyroidism leads to reduced esophageal — which refers to the food pipe — and gastric motor activity that can cause gastric dysfunction, such as constipation.

Another study from 2014 also noted that constipation is a common symptom of hypothyroidism. Similar to the 2009 study, the study authors noted that issues with motor dysfunction might account for the increased rate of constipation in people with hypothyroidism.

Both forms of thyroid issues may share a connection to gut health.

According to a 2021 meta-analysis, the gut microbiome may affect the development of autoimmune thyroid diseases. These conditions, such as Graves’ disease and Hashimoto’s thyroiditis, can lead to hyperthyroidism and hypothyroidism, respectively.

Therefore, keeping the gut healthy may help prevent thyroid issues, which, in turn, may reduce any gastrointestinal effects.

Treatment for hyperthyroidism may involve:

  • Medications: Beta-blockers can help treat symptoms, while antithyroid medications can help reduce the amount of thyroid hormones the body produces.
  • Radioiodine therapy: This treatment uses radioactive iodine to slowly destroy the thyroid tissue responsible for making hormones.
  • Surgery: This involves the surgical removal of part or all of the thyroid.

People need to discuss their treatment with their doctor to discuss possible benefits and side effects so they can adjust to the treatment if necessary.

Treatment for hyperthyroidism will vary according to several factors, including:

  • underlying causes or risk factors
  • the severity of the condition
  • age
  • possible allergies to medications
  • presence of other conditions
  • experience of doctors working with a person

Constipation treatments

If constipation occurs in people with hypothyroidism, treatment often involves dietary changes. This may include increasing fluids and increasing fiber intake. A person may also find that exercise can help improve constipation.

A doctor may also recommend using over-the-counter or prescription laxatives to help someone pass stool. They may also examine their medications and supplements and recommend which medications to stop or change to help alleviate constipation.

Hyperthyroidism does not typically lead to constipation, but hypothyroidism can. The former can cause more frequent and loose bowel movements.

A person with hyperthyroidism will likely need treatment to address their underlying condition. They may also benefit from medications to help alleviate their symptoms and reduce the number of hormones their body has. With treatment, they should notice a reduction in hyperthyroidism symptoms.

Constipation may resolve with lifestyle changes, such as eating more fiber and increasing fluid intake. In some cases, medications or changing current medications may help.

If a person has either condition, they can talk with a doctor if they experience issues that may indicate thyroid problems or constipation. A doctor can help diagnose and treat the conditions.