What Causes Constipation? Understanding the Root Causes, From Lifestyle to Underlying Conditions

Constipation is rarely a mystery and often has one or more identifiable reasons behind it. Whether it has crept up gradually over months or appeared unexpectedly in a matter of days, understanding the cause is an important step toward finding the right relief.

What Causes Constipation?

Constipation is usually caused either by how the bowel works, or by an external factor. Constipation is generally understood as having fewer than three bowel movements a week, though it can also involve straining, hard stools, or a feeling of not fully emptying the bowel. ¹ When these difficulties persist for six months or more, with active symptoms in the past three months, it is considered chronic. ¹ Chronic constipation is either primary or secondary. ¹

Primary (functional) constipation — the most common form — arises from problems within the colon or the muscles and nerves that control it. ¹ There are three subtypes:

Normal-transit constipation, where stool moves through the colon at a typical speed. People can still feel bloated, uncomfortable, or like they haven’t fully emptied their bowels, just as others with chronic constipation do. ^1,3
Slow-transit constipation involves delayed passage of stool through the colon. ²
Defecatory disorders, also known as Pelvic floor dysfunction. The muscles involved in having a bowel movement fail to coordinate properly, blocking the passage of stool even when it is ready to pass. ¹

Secondary constipation is caused by an external factor — typically a medication, a systemic disease, or a structural issue in the bowel. ¹ Identifying a secondary cause is critical because treating the underlying cause may resolve the constipation entirely.

What Causes new onset Constipation?

New onset constipation usually has a specific trigger and is more likely than gradual constipation to have an identifiable cause. ³

A common reason is a change in routine or circumstance: starting a new medication, a significant change in diet, or a period of heightened stress or emotional upheaval, for example. ^3,4

Emotional events can also trigger new onset constipation. Significant stress — bereavement, change of environment, hospitalisation — affects communication between the brain and the gut, slowing bowel function in a way that can feel very physical. ⁴ Acknowledging this connection can reduce both confusion and embarrassment about the symptom.

If constipation comes on suddenly and does not have an obvious explanation, or if it is accompanied by symptoms such as blood in the stool, unexplained weight loss, abdominal pain, or a noticeable change in what your stools look like, it is worth speaking to a doctor or pharmacist. ³

What Could Be Causing Constipation?

For many people, constipation reflects a combination of factors rather than a single cause.

Diet and hydration. A diet lacking in dietary fibre — the plant material that adds bulk to stool and stimulates the colon — is a commonly identified cause. Similarly, not drinking enough fluids means that the colon absorbs more water from the stool, making it firm and difficult to pass. ²

Physical inactivity. A sedentary lifestyle, long periods of bed rest, or reduced mobility are associated with a higher likelihood of constipation, though the exact relationship between physical activity and bowel function is not fully understood. Regular movement is generally encouraged as part of a healthy lifestyle and may help support bowel regularity in some people. ²

Medications. Some medicines can cause or worsen constipation as a side effect. These include strong painkillers such as opioids, certain antidepressants, calcium channel blockers used for heart conditions and blood pressure, and iron supplements. ² When a new medication known to slow bowel motility is started at the same time as constipation begins, the drug may be the cause. ³

Ignoring the urge to go. Regularly putting off a bowel movement — whether due to a busy schedule, discomfort using public toilets, or pain when going — can over time reduce your body’s natural urge to go, and may lead to stools becoming harder and more difficult to pass. ⁴

Emotional state. Anxiety, depression, and stress are each linked to constipation — and this is a genuine physical connection, not something imagined. ⁴ The brain and gut are in constant communication, and emotional distress can directly affect how the bowel works.

Hormonal changes. Hormonal factors can influence bowel function in some people. During pregnancy, for example, hormonal changes are known to slow the movement of the gut, which can contribute to constipation. ⁴

What Is the Root Cause of Chronic Constipation?

The phrase “root cause” implies a single explanation, but chronic constipation often has several interacting causes rather than one. ⁴ That said, understanding the underlying mechanism is essential for finding the right treatment.

For many people with functional constipation, the root cause lies in how the colon moves stool. In slow-transit constipation, the colon generates fewer and weaker propulsive contractions, resulting in prolonged transit and dry, hard stools. ^1,2 This may reflect reduced signalling from the gut’s own nerve network, or a reduction in the specialised pacemaker cells that drive coordinated gut muscle contractions. ¹

Where a coordination problem is the cause, the pelvic floor muscles should relax when someone tries to have a bowel movement, but instead they tighten or fail to relax fully — creating resistance at the outlet that blocks stool from passing. ¹ This pattern can develop following pelvic floor injury or childbirth, or it may arise with no obvious cause at all. ¹

In secondary constipation, the root cause lies outside the colon — in a medication, a hormonal imbalance, a neurological disease, or a structural abnormality — and no amount of fibre or lifestyle modification will fully resolve the problem until that underlying cause is addressed. ¹

Which Organs or Body Systems Can Cause Constipation?

Constipation is frequently assumed to be purely a bowel problem, but multiple body systems can drive it — which helps explain why it so often accompanies other health conditions. ²

The nervous system. The gut has its own network of nerves that controls how it moves and functions. When this nerve network is affected — whether by changes in the gut’s own nerve cells or by a disease affecting the wider nervous system — it can contribute to chronic constipation. Conditions including Parkinson’s disease, multiple sclerosis, stroke, and spinal cord injury are all associated with constipation. ^1,2

The hormonal and metabolic system. Several hormonal and metabolic conditions can slow bowel function. An underactive thyroid slows the body’s processes generally, including in the gut, and is a recognised but often overlooked cause of constipation. Diabetes can also affect bowel function through its effects on the nervous system. Imbalances in certain minerals in the blood — such as calcium or potassium — can also contribute. ^1,2

Connective tissue conditions. Connective tissue conditions such as systemic sclerosis (scleroderma) and amyloidosis are associated with constipation, typically alongside other features of these conditions. ¹

The colon and rectum directly. Structural problems within the colon or rectum can also cause constipation. These include narrowing or blockages within the bowel, and anatomical changes such as rectal prolapse (where part of the rectum slips out of place), or a rectocele (where part of the bowel wall bulges out of place). ^1,3,5 These structural causes are less common than functional ones but are important to exclude, particularly in cases of new or progressive constipation.

The psychological system. There is a clear link between psychological factors and constipation — people with constipation more often experience anxiety, stress, and depression, and psychological distress can contribute to constipation symptoms. Constipation can also have a significant impact on quality of life. ⁴ This connection is well recognised and is one reason why emotional health is worth considering as part of the broader picture when constipation is difficult to manage.

What You Can Do

If you are experiencing constipation, starting with some practical changes is a sensible first step. Gradually increasing dietary fibre to around 25–30 g per day is well supported by the evidence. ¹ Staying reasonably active and ensuring you are drinking enough fluids throughout the day may also help, particularly if your current intake is low. ² Responding promptly when you feel the urge to have a bowel movement — rather than putting it off — can help keep your body’s natural urge to go working normally over time. ⁴ If these measures aren’t enough on their own, laxatives may also help. ^1,3

If constipation persists despite these changes, or if you notice any of the symptoms described earlier — such as blood in the stool, unexplained weight loss, or abdominal pain — speak with a doctor or pharmacist. ³

Conclusion

FAQ

For most people, constipation involves a combination of factors rather than a single cause. A diet low in dietary fibre is one of the most consistently identified, as fibre adds bulk to stool and helps keep the bowel moving. ² Not drinking enough fluids and being less physically active may also play a role, particularly where there is a genuine deficiency in either. ² Medications are also a very common cause — particularly opioid painkillers — and this is especially true in older adults who take multiple medicines at the same time. ²

Yes — anxiety, depression, and chronic stress are each linked to constipation, and this is a genuine physical connection, not something imagined. ⁴ The brain and gut are in constant communication, and emotional distress can directly affect how the bowel works. Supporting emotional wellbeing is therefore a legitimate part of managing constipation.

New onset constipation is more likely than gradual constipation to have an identifiable cause. ³ Starting a new medication, a change in diet, or a period of intense stress are among the most common explanations. ^2,4 However, new-onset constipation that persists, worsens, or is accompanied by blood in the stool, unexplained weight loss, abdominal pain, or a noticeable change in what your stools look like should be assessed by a doctor, as it may signal a cause that needs investigation. ³

Several conditions are known causes of constipation. Neurological disorders — particularly Parkinson’s disease, multiple sclerosis, and diabetes with autonomic neuropathy — are among the most common. ² Hypothyroidism is a frequently overlooked hormonal cause. ² Irritable bowel syndrome (constipation-predominant type), systemic sclerosis, and structural problems within the bowel such as narrowing or blockages can also cause constipation. ¹ If constipation is persistent and does not respond to lifestyle changes, these should be screened for. A family history of bowel cancer or inflammatory bowel disease is also worth mentioning to your doctor, as this may affect the investigations they recommend. ^3,5

Yes, drug-induced constipation is common, especially in older adults taking multiple medicines. ² Opioid painkillers are the most potent offenders, but anticholinergic drugs, calcium channel blockers, iron supplements, and certain antidepressants are all frequently associated with constipation. ² If constipation began around the time a new medication was started, this connection is worth raising with a prescribing doctor or pharmacist, who may be able to adjust the treatment.

The gut has its own network of nerves that controls the muscle contractions which move stool through the bowel. When this nerve network is damaged or disrupted — whether by a disease affecting the gut directly or by a condition affecting the wider nervous system — bowel function can slow down significantly. ¹ In slow-transit constipation, there is evidence that some of the specialised cells that drive these contractions are reduced in number. ¹ Conditions such as Parkinson’s disease, multiple sclerosis, and spinal cord injury can all affect gut motility in this way. ²

Yes — an underactive thyroid is a recognised cause of constipation. ² When thyroid hormone levels are low, the body’s processes slow down, and this can include the movement of the gut. In some cases, treating the underlying thyroid condition may help to resolve the constipation. If you have persistent, unexplained constipation, it is worth mentioning to your doctor, who can decide whether checking your thyroid function is appropriate. ⁵

No — while the colon plays a central role in moving stool toward the rectum, constipation can originate in the rectum and pelvic floor, in the nervous system, in the hormonal system, or as a result of structural problems elsewhere in the bowel. ¹ In some cases, for instance, the problem is not that stool is moving too slowly through the colon, but that the pelvic floor muscles fail to relax properly when a person tries to have a bowel movement — creating a blockage even when the stool is ready to pass. This distinction matters because the treatments for these different types differ considerably.

In most cases, constipation is not a sign of a serious underlying condition and responds well to lifestyle changes or appropriate treatment. ¹ However, certain accompanying symptoms — blood in the stool, unexplained weight loss, progressive abdominal pain, or new-onset constipation— can indicate a condition that needs medical evaluation. ^3,5 If you notice any of these alongside your constipation, speak with a healthcare professional promptly.

Lactulose is an osmotic laxative. ⁶ Once it reaches the colon, it is broken down by gut bacteria, which draws water into the bowel. This softens the stool, increases its volume, and stimulates the wave-like muscle contractions that move stool through the bowel. ⁶ It typically takes 2 to 3 days before the full benefit is seen, so it is important to give it time to work. ⁶ A pharmacist or doctor can advise on the right dose and whether it is suitable for you if you have any questions.

This article was written with the assistance of generative AI technology and reviewed for accuracy.