Can Hypothyroidism Cause Constipation? What You Need to Know

Medically reviewed by: Dr. Tom Babu, Consultant Diabetologist & Endocrinologist - Written by Riya Yacob - Updated on 9/10/2026

Yes, an underactive thyroid can cause constipation. When the thyroid makes less hormone than the body needs, the muscles of the gut move food along more slowly, stools become harder, and bowel movements become less frequent. Thyroid and constipation are commonly linked, and the digestive symptoms usually ease once hormone levels return to a healthy range with treatment.

Key Takeaways

• Low thyroid hormone slows the gut, which is why hypothyroidism constipation develops
• Constipation rarely appears alone, so look for tiredness, dry skin, feeling cold and weight gain
• A TSH test and a free T4 test confirm the cause
• Treatment of the thyroid usually improves bowel habits, and fibre, fluids and movement support the process
• Persistent constipation deserves a medical review, even when a thyroid cause seems unlikely

Constipation is easy to put down to diet or a busy routine, yet thyroid and constipation are closely connected, and many people only learn this after a blood report. In this blog, we explain how low thyroid hormone affects digestion, which other changes appear alongside it, how doctors confirm the cause and what helps. 

Can Hypothyroidism Cause Constipation?

It can. Thyroid hormones set the pace for many body processes, including the movement of the intestines. When levels drop, the whole system runs at a slower speed.

How Low Thyroid Hormone Slows the Gut

The intestines move food forward through a series of gentle muscle contractions. Thyroid hormone supports these contractions. With low free T4, the contractions weaken, and food spends more time in the bowel. The colon absorbs extra water from the stool during that time, so it turns hard and dry and becomes harder to pass.

This explains why underactive thyroid and constipation often appear together, and why constipation and thyroid problems are discussed as a pair in medical practice. Researchers group these changes under thyroid problems and digestion, since bloating, a feeling of fullness and slower stomach emptying can accompany the sluggish bowel.

Other Factors

Lower energy levels often mean less physical activity, and a slower metabolism can reduce appetite and fluid intake. Some medicines, including iron and calcium supplements, can also slow the bowel. These factors combine with low hormone levels, so thyroid-related constipation may need more than one adjustment to settle.

Other Signs That Point to an Underactive Thyroid

Constipation by itself has many possible causes. It becomes clearer when other hypothyroidism symptoms appear around the same time, and the common underactive thyroid symptoms and signs of hypothyroidism include:

• Tiredness that continues after a full night's sleep
• Weight gain with an unchanged diet
• Feeling cold when others feel comfortable
• Dry skin and thinning hair
• Muscle aches and joint stiffness
• A slower heartbeat
• Low mood or difficulty concentrating
• Heavier or irregular periods in women
• Swelling at the front of the neck

Symptoms develop gradually, sometimes over years, which makes them easy to attribute to age or stress. A person with three or four of these changes alongside constipation may benefit from a blood test.

Who is More Likely to Notice Thyroid-Related Constipation?

Women and older adults are diagnosed with hypothyroidism more frequently than others. The most common cause in adults is Hashimoto's thyroiditis, an autoimmune condition in which the body's defence system gradually reduces the thyroid's ability to make hormone. This leads to primary hypothyroidism, where the gland itself is the source of the shortfall.

A milder stage, called subclinical hypothyroidism, shows a raised TSH while the thyroid hormone level still sits in the usual range. Some people at this stage notice mild constipation and tiredness, while others notice nothing. A doctor decides on treatment by looking at the symptoms, the antibody results and the trend over repeat tests.

How Doctors Confirm the Cause

Hypothyroidism diagnosis starts with a conversation about symptoms, family history and medicines, followed by a physical examination. A thyroid blood test then provides the confirmation. Most laboratories report a thyroid function test panel that includes TSH and free T4, and some add antibody levels.

Who is More Likely to Notice Thyroid-Related Constipation?

Women and older adults are diagnosed with hypothyroidism more frequently than others. The most common cause in adults is Hashimoto's thyroiditis, an autoimmune condition in which the body's defence system gradually reduces the thyroid's ability to make hormone. This leads to primary hypothyroidism, where the gland itself is the source of the shortfall.

A milder stage, called subclinical hypothyroidism, shows a raised TSH while the thyroid hormone level still sits in the usual range. Some people at this stage notice mild constipation and tiredness, while others notice nothing. A doctor decides on treatment by looking at the symptoms, the antibody results and the trend over repeat tests.

How Doctors Confirm the Cause

Hypothyroidism diagnosis starts with a conversation about symptoms, family history and medicines, followed by a physical examination. A thyroid blood test then provides the confirmation. Most laboratories report a thyroid function test panel that includes TSH and free T4, and some add antibody levels.

The pituitary gland releases TSH to signal the thyroid to make more hormone. When the thyroid slows, the pituitary raises its signal, so high TSH levels are usually the first sign on a report. A TSH test is therefore the standard starting point, and a free T4 test shows how much active hormone is circulating. Reference ranges differ between laboratories, so results are best read with a doctor.

Managing Constipation Alongside Thyroid Treatment

Thyroid Treatment

Doctors commonly prescribe levothyroxine, a daily tablet that replaces the missing hormone. As levels return to a healthy range over a few weeks to months, bowel movements usually become more regular. Doses are adjusted using repeat blood tests, and timing matters: the tablet works best on an empty stomach, taken at a consistent hour, with a gap before iron or calcium supplements.

Daily Habits That Help

While treatment takes effect, simple routines support the bowel:

• Eat fibre from vegetables, fruit, oats, pulses and whole grains, and increase the amount gradually
• Drink water through the day, following any limits your doctor has set
• Walk for 20 to 30 minutes most days
• Keep a regular toilet routine, ideally after a meal
• Raise the feet on a small stool to ease the position of the bowel

Laxatives are best used with medical advice, since the right choice depends on age, other medicines and general health.

How Common is Hypothyroidism in India?

A study across 8 Indian cities, published in the Indian Journal of Endocrinology and Metabolism, found hypothyroidism in 10.95% of adults, close to 1 in 10. About 3.47% of the people studied were identified with the condition for the first time during the survey. The figures show that many people live with an underactive thyroid for some time before a test gives the answer, which is one reason symptoms such as constipation deserve attention.

When to See a Doctor

Book a consultation if constipation lasts longer than three weeks, returns repeatedly or comes with tiredness, weight changes or dry skin. Seek prompt medical review for blood in the stool, severe abdominal pain, vomiting or unexplained weight loss, as these signs need separate evaluation. Anyone already on thyroid medication whose constipacontact Silverline Hospitation continues should have the dose checked.

Conclusion

Thyroid and constipation are connected through the way thyroid hormone controls the speed of the gut. When the hormone level falls, digestion slows, and constipation is one of the earliest changes people notice. A simple blood test gives a clear answer, and treatment usually brings steady improvement in bowel habits. Combined with fibre, fluids and regular movement, most people find their routine returns to normal.

Book a Thyroid Check at Silverline Hospital

If constipation has been part of your routine along with tiredness or other changes, a thyroid blood test can show whether the cause lies there. For more about thyroid treatment and consultation, contact Silverline Hospital.

Frequently Asked Questions (FAQs)

Q1: Can an underactive thyroid cause constipation?
A1: Yes. Low thyroid hormone slows the muscles of the intestine, so stools move along slowly and become dry and hard. This is one of the more common digestive effects of hypothyroidism.

Q2: Will constipation go away once the thyroid is treated?
A2: For most people, yes, though it takes some time. Levothyroxine brings hormone levels back to a healthy range over several weeks, and bowel movements usually become more regular as that happens. Your doctor will repeat the thyroid blood test to confirm that the dose suits you. Fibre, fluids and daily walking help during this period. If constipation continues after the levels are steady, other causes such as diet, medicines or a separate digestive condition should be reviewed.

Q3: Which tests check for thyroid and constipation links?
A3: A thyroid function test is the usual starting point. It measures TSH and free T4, and a high TSH with a low free T4 points to primary hypothyroidism. Your doctor may add an antibody test to check for Hashimoto's thyroiditis, along with other tests to rule out different causes of constipation.