When you have hyperthyroidism, it can make your body’s “fight or flight” system work too much and cause diarrhea and other gastrointestinal (GI) tract symptoms. These may include frequent bowel movements and malnutrition

Your thyroid is a small gland in your neck that produces hormones called thyroxine (T4) and triiodothyronine (T3), which play a role in your metabolism.

Hyperthyroidism happens when your thyroid produces too much of these hormones, speeding up your metabolism. Causes of hyperthyroidism include conditions like Graves’ disease, too much iodine consumption, or harmless nodules that grow on the thyroid.

Hyperthyroidism can affect typical bodily functions, including your GI tract, resulting in symptoms like diarrhea.

Read on to learn more about why hyperthyroidism can cause diarrhea and other GI symptoms, how to treat and prevent diarrhea from hyperthyroidism, and when to seek immediate medical help for your symptoms.

The thyroid gland is one of the main organs that plays a role in your metabolism. Metabolism is how your body consumes and uses energy from food and other sources.

Another process that plays a role in your metabolism is the sympathetic nervous system. This part of your nervous system manages your “fight or flight” response by raising your energy levels, as well as nerve responses in organs throughout your body.

The thyroid has a close connection to these responses of sympathetic nervous system. With hyperthyroidism, the thyroid produces too many T4 and T3 hormones, overstimulating the nerves that manage your digestive tract.

When your bowel nerves are overstimulated, they can increase your intestinal motility, which refers to the movement and contraction of muscles in the intestines. This causes your bowel muscles to contract more quickly than usual and push food through before it’s fully digested. This also prevents fluids from being fully absorbed from food as it passes through, leading to watery diarrhea.

Hyperthyroidism also has links to other GI tract problems that can result from increased metabolism.

Hyperthyroidism and frequent bowel movements

Hyperthyroidism doesn’t always cause diarrhea. But increased movements in your intestines can make you feel like you have to go to the bathroom more often.

Having more frequent bowel movements than you’re used to can irritate tissues and muscles around your rectum and anus.

Having frequent bowel movements over a long period of time can lead to complications like:

Hyperthyroidism and malabsorption

When food passes through your digestive tract too quickly, your intestines don’t have enough time to absorb nutrients from your food. This is called malabsorption. Inflammation that may result from hyperthyroidism can also keep your intestines from absorbing nutrients as usual, leading to malnutrition.

Over time, you may not get enough nutrients and experience malnutrition. The longer you experience malnutrition, the more likely organs throughout your body might stop functioning as usual.

Experts recommend seeking medical help if you have any of the following symptoms of hyperthyroidism along with diarrhea that lasts for more than a day:

Some of these symptoms result from an emergency condition called a thyroid storm. This happens when you suddenly experience severe symptoms related to hyperthyroidism that affect important functions like your breathing and heart rate.

To help prevent diarrhea as a result of hyperthyroidism, healthcare professionals may recommend medications like methimazole (Tapazole, Northyx) to slow down your bowel muscles.

Antithyroid medications help keep your thyroid from producing too much T4 and T3. Drugs like methimazole and propylthiouracil are considered safe for most people and can lower symptoms linked to hyperthyroidism.

For severe cases of hyperthyroidism, a doctor may suggest a thyroidectomy to remove part or all of your thyroid gland. Doctors usually recommend this procedure when other treatments haven’t worked or if thyroid nodules cause hyperthyroidism.

Treating hyperthyroidism can help you prevent diarrhea caused by hyperthyroidism.

But if you’re still having diarrhea even when you’re receiving treatment for hyperthyroidism, you can try some of these home remedies to help prevent diarrhea:

  • Try to drink plenty of water, especially after long episodes of diarrhea that can dehydrate you.
  • Take probiotics for diarrhea to help promote “good” gut bacteria and improve digestion.
  • Use Pepto-Bismol or Imodium as needed to help with fluid absorption and reduce inflammation in the intestines.
  • Include a low fiber BRAT diet (bananas, rice, applesauce, and toast) in your routine to help slow down digestion.
  • Try to avoid foods that can cause diarrhea, such as high fiber wheat products or dairy.

Hyperthyroidism can overstimulate the sympathetic nervous system and cause diarrhea and other gastrointestinal (GI) tract symptoms. These may include frequent bowel movements and malnutrition.

If you have constipation that’s painful or lasts for more than a few days, it’s advisable to seek medical help.