Last Updated on April 26, 2026
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Constipation is one of the most common digestive complaints worldwide, and yet it is often misunderstood, underreported, and therefore, poorly managed. This may be because it is one of those symptoms that can feel “minor” until it starts affecting your comfort, appetite, mood, and daily routine.
If you have thyroid disease (hypothyroidism especially), constipation deserves extra attention because low thyroid hormone can slow many body processes, including gut motility.
In this article:
- What counts as constipation? Is it about “going less often”?
- Why and how does constipation happen?
- What’s the connection between constipation and hypothyroidism?
- What are some “red flags” to take note of? When does constipation need medical assessment?
- What are some common, evidence-backed strategies that actually help with constipation?
- An important point of consideration about levothyroxine timing
What counts as constipation? Is it about “going less often”?
According to the American College of Gastroenterology, many people assume constipation means “not pooping every day.” But normal bowel frequency actually varies a lot. Constipation is more about difficulty and discomfort than a specific number (although that also counts to some extent).
Clinicians often use the Rome IV criteria to define functional constipation. In simple terms, it includes symptoms like straining during bowel movements, hard stools, feeling of incomplete emptying, blockage sensation, manual maneuvers, and infrequent stools (fewer than 3 bowel movements per week), occurring regularly for months (3 months or longer).
Want to do a quick self-check?
The Bristol Stool Chart is a helpful visual tool:
- Types 1–2 (hard pellets or lumpy sausage) often suggest constipation.
- Types 3–4 are typically considered “ideal.”
Why and how does constipation happen?
To better understand constipation, it helps to at least know a little about how digestion normally works.
Your colon (large intestine) moves stool forward using rhythmic muscle contractions called peristalsis. As stool moves, water is absorbed, forming a soft but solid bowel movement.
Constipation can occur when the colon moves too slowly, too much water is absorbed, or the muscles of the rectum or pelvic floor don’t coordinate properly. The result? Stool becomes dry, hard, and difficult to pass.
Based on these patterns, constipation usually falls into one (or a mix) of these categories:
1. Slow-transit constipation (the colon moves too slowly)
Stool sits longer in the colon, water gets absorbed, and stool becomes drier or harder.
2. Outlet constipation (pelvic floor “coordination” issue)
Sometimes the issue isn’t stool moving through the colon. It’s actually the final step. The pelvic floor and anal sphincter may not relax properly during a bowel movement (often called dyssynergic defecation). Biofeedback-based pelvic floor therapy is commonly considered a treatment of choice for this pattern.
3. Secondary constipation (a symptom of something else)
This is where thyroid disease, medications and supplements, dehydration, neurological disorders, metabolic issues, and more come in.
Did you know that low fiber intake is one of the most common causes of constipation worldwide? Dietary fiber adds bulk and holds water in stool, making it easier to pass. This also explains why dehydration can lead to excessive water reabsorption in the colon. According to the United States Department of Agriculture’s Dietary Guidelines for Americans 2020–2025, the recommended intake of dietary fiber for those below age 51 is about 25 g/day for women and 38 g/day for men, and interestingly, most adults consume less than half of this.
As far as medications and supplements are concerned, here are a few that have some documented risk of triggering or worsening constipation:
- Iron supplements
- Calcium supplements
- Opioids
- Antidepressants
- Antihistamines
- Some blood pressure drugs
It is worth noting that these aren’t all the possible causes or triggers of constipation. In fact, something as seemingly trivial as ignoring the urge to go can also be problematic. Research has shown that repeatedly suppressing the urge to defecate reduces rectal sensitivity over time and worsens constipation.
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Download ThyForLife for FreeWhat’s the connection between constipation and hypothyroidism?
Constipation is one of the classic symptoms of hypothyroidism. Normally, thyroid hormones regulate many bodily functions such as metabolism and energy production, as well as muscle contraction and nerve function. When thyroid hormone levels are low,
- intestinal muscle contractions slow down
- gut transit time increases
- more water is absorbed from stool
- stool becomes hard and difficult to pass
These are pretty much the same underlying mechanisms of constipation we saw in the previous section.
A 2024 review article on thyroid disorders and abnormal gastrointestinal movement explains how thyroid dysfunction is associated with changes in motility in the digestive tract. It highlights that both hyperthyroidism and hypothyroidism can disrupt normal movement in any part of the GI system.
Constipation, in particular, may appear even in mild or subclinical hypothyroidism, and often improves once thyroid hormone levels are properly treated.
If constipation is new, persistent, or worsening, especially with other hypothyroid symptoms (such as fatigue, feeling cold, dry skin, and brain fog), you should discuss a thyroid check with a clinician. A blood test is the only way to confirm hypothyroidism.
What are some “red flags” to take note of? When does constipation need medical assessment?
Most constipation is manageable. In fact, occasional constipation is fine. Chronic constipation, however, is not.
You should seek medical attention if constipation is:
- lasting longer than 3 months
- severe or worsening
- accompanied by severe abdominal pain, bloating, nausea, vomiting, fever, or symptoms of bowel obstruction
- associated with unexplained weight loss
- associated with visible blood in stool (or persistent rectal bleeding) or black/tarry stool
- associated with a new change in bowel habits that persists (especially if you’re an older adult)
- associated with iron-deficiency anemia
In hypothyroid individuals, persistent constipation may indicate:
- inadequate thyroid hormone replacement
- poor medication absorption
- gut motility dysfunction
Also, note that rectal bleeding and iron-deficiency anemia are well-established alarm features for colorectal cancer evaluation.
What are some common, evidence-backed strategies that actually help with constipation?
1. Treating the underlying thyroid condition
For hypothyroidism, proper levothyroxine (thyroid hormone replacement) dosing cannot be overemphasized. If constipation persists despite treatment, hormone levels (TSH, FT4, and FT3) should be reassessed. If they are normal, the constipation is most likely due to something other than the thyroid.
2. Fiber intake
Fiber can improve stool bulk and consistency, especially if your baseline intake is low. The joint 2023 American College of Gastroenterology (ACG) and American Gastroenterological Association (AGA) guideline suggests fiber supplementation for chronic idiopathic constipation. (This is a conditional recommendation. To read more about the guideline, click here).
Here are some practical tips:
- Increase fiber gradually over 1–2 weeks to reduce gas or bloating.
- Fiber works best when paired with enough fluids.
- If you take levothyroxine, high-fiber diets and supplements can interfere with absorption for some people. Timing greatly matters. (More below).
Here are some best sources of fiber:
- Vegetables.
- Fruits (such as kiwi, pears, berries, and apples).
- Legumes.
- Whole grains.
- Psyllium husk. It tends to be better supported than some other fibers for constipation and stool form.
3. Hydration
It’s true that fluids help fiber work and can reduce stool hardness. In fact, without enough water, fiber can actually worsen constipation by creating hard, difficult-to-pass stools, so adequate fluid intake (like water) is crucial to make fiber effective for regularity. However, simply “drinking more water” may not fix constipation if motility or pelvic floor coordination is the main issue.
How much should you aim for then? It’s actually not so simple because there’s no universal rule, since hydration needs vary from person to person. Your needs depend on factors like body size, activity level, climate, and overall health. As a general guideline, most adults can aim for at least 1.5–2 liters of fluids per day. If you’re physically active, live in a hot climate, or sweat a lot, you’ll likely need more.
4. Regular physical activity and established bowel routine
The colon is most active after meals. This is also known as gastrocolic reflex. For many, the best time to try is after breakfast. So you may want to just sit, relax, and allow time. Beyond this, regular physical activity can support bowel regularity. Even 20–30 minutes of walking daily can improve bowel motility. Also, as mentioned before, don’t ignore the urge repeatedly. It’s understandable that it might be tempting to do that if you’re busy or not at home, but it really doesn’t help.
5. Osmotic laxatives
For many adults with chronic constipation, polyethylene glycol (PEG) is strongly recommended by the ACG/AGA guideline. PEG works by holding water in the stool, making it softer and easier to pass. The guideline also suggests the use of magnesium oxide, which also draws water into the intestines and softens stool. It is worth pointing out that magnesium can be risky with kidney disease.
6. Senna (a stimulant laxative)
The same ACG/AGA guideline includes senna (This recommendation is conditional). Remember that stimulant laxatives like senna can be effective, but they’re not ideal for everyone. For instance, they can cause cramping. For long-term use, it’s best to do this with clinician guidance.
7. Pelvic floor therapy
If you often have prolonged straining, a strong feeling of incomplete emptying, the need to use manual maneuvers, or a sense of outlet blockage, you could ask your healthcare provider about a possible evaluation for pelvic floor dysfunction or dyssynergia. Biofeedback-based therapy is commonly highlighted as beneficial for this condition.
8. Improving toilet posture
Because modern toilets tend to put the rectum at an unnatural angle, using a footstool to elevate your feet could at least mimic a squatting position and straighten the rectum. This could make bowel movements easier.
An important point of consideration about levothyroxine timing
If you take levothyroxine, constipation management may inadvertently cause issues with medication absorption. Research has shown that certain supplements and foods (notably calcium, iron, and sometimes fiber, coffee, and soy) can reduce levothyroxine absorption for some people.
A practical approach many clinicians recommend is taking levothyroxine on an empty stomach and separating it from interfering supplements by several hours (your prescriber’s instructions should be the priority). You can read more about this from the guidelines by the American Thyroid Association (ATA) published in 2014.
Why does this even matter? If constipation leads you to start fiber supplements, magnesium, or iron (for anemia), it’s worth checking timing so your thyroid treatment stays stable.
Key takeaways
- Constipation is not just “not going often.”
- It is a functional digestive disorder defined by a combination of symptoms.
- It is diagnosed using the Rome IV criteria, which require at least two of these symptoms for 3 months or longer.
- Low thyroid hormone levels can cause intestinal hypomotility.
- The good news is that constipation is highly manageable with proper thyroid treatment (if the thyroid is the cause), diet and lifestyle changes, and evidence-based medical support.
- If constipation is persistent, severe, or affecting your quality of life, it deserves proper medical attention.
