Overflow Diarrhoea From Constipation: Causes, Symptoms and Relief

Overflow diarrhoea can seem contradictory. Diarrhoea is usually associated with loose, frequent stools, while constipation is associated with hard or infrequent bowel movements. However, it is possible to experience both at the same time.

When a large amount of hard stool builds up in the rectum, softer or watery stool can sometimes leak around it. This is known as overflow diarrhoea and can be a sign of faecal impaction, where stool has become stuck and cannot be passed normally.

Because the stool being passed is loose, overflow diarrhoea can easily be mistaken for ordinary diarrhoea. Treating the diarrhoea alone may therefore miss the underlying problem.

This guide explains why overflow diarrhoea happens, what symptoms to look for, how faecal impaction is treated, when home measures may be appropriate and when you should seek medical advice.

What Is Overflow Diarrhoea?

Overflow diarrhoea happens when liquid or softer stool passes around a build-up of hard stool in the rectum.

The underlying problem is usually constipation rather than ordinary diarrhoea.

A typical sequence is:

1. Stool remains in the bowel or rectum for longer than usual.

2. More water is absorbed from it.

3. The stool becomes increasingly hard and difficult to pass.

4. A large mass of stool can become lodged in the rectum.

5. Softer or watery stool higher in the bowel may then leak around the hardened stool.

This leakage can look like diarrhoea, but the bowel may still contain a significant amount of retained stool.

That is why someone with overflow diarrhoea may experience a mixture of symptoms, such as watery stool on one occasion and hard, difficult-to-pass stool on another.

Overflow diarrhoea is particularly associated with faecal impaction, although not every episode of loose stool in someone who is constipated means that impaction is present.

The important point is that passing liquid stool does not necessarily mean the bowel has emptied properly.

What Does Overflow Diarrhoea Look Like?

Overflow diarrhoea can be confusing because the stool may appear loose or watery even though constipation is still present.

Possible signs include:

• Small amounts of loose or watery stool

• Leakage or soiling between bowel movements

• Hard stool at other times

• Straining to open your bowels

• Feeling that stool is stuck

• A sensation of incomplete emptying

• Abdominal bloating or discomfort

• Passing only small amounts of stool despite feeling the need to go

Some people experience alternating bowel movements, with episodes of watery stool followed by hard, difficult-to-pass stools.

A key sign is that the loose stool does not seem to result in a proper bowel movement or a feeling of complete emptying.

Why It Can Be Mistaken for Ordinary Diarrhoea

The appearance of liquid stool can make it seem as though the bowel is moving too quickly. With overflow diarrhoea, however, the opposite may be happening.

Hard stool can remain lodged in the rectum while softer stool from further up the bowel moves around it.

This is why treating the symptom as ordinary diarrhoea without considering constipation can sometimes miss the underlying problem.

If loose stools occur alongside a history of constipation, straining, hard stools or a persistent feeling of incomplete emptying, faecal loading or impaction may need to be considered.

Overflow Diarrhoea vs Ordinary Diarrhoea

Overflow diarrhoea and ordinary diarrhoea can both involve loose or watery stool, but the underlying causes are very different.

With overflow diarrhoea, the main problem is usually retained hard stool or faecal impaction. Liquid stool passes around the blockage, which can create the appearance of diarrhoea even though the bowel has not emptied properly.

Ordinary acute diarrhoea, by contrast, usually happens because the bowel is moving contents through too quickly or because excess fluid is being secreted into the intestine.

Why the Difference Matters

If overflow diarrhoea is mistaken for ordinary diarrhoea, the underlying constipation may be overlooked.

This is particularly important because medicines intended to slow bowel movements are not necessarily appropriate when hard stool is already retained.

If watery stool occurs alongside constipation, abdominal bloating, straining, hard stools or a persistent feeling that the bowel has not emptied, it is worth considering whether the diarrhoea could be related to faecal loading rather than treating it automatically as ordinary diarrhoea.

What Causes Overflow Diarrhoea?

Overflow diarrhoea usually develops because hard stool has built up in the rectum and softer or liquid stool is passing around it. The immediate problem is therefore often faecal loading or faecal impaction, but several factors can contribute to that build-up.

Long-Term or Severe Constipation

The most direct cause is constipation that has allowed stool to remain in the bowel for too long.

As stool sits in the colon, more water is absorbed from it. This can make it progressively harder, drier and more difficult to pass. If enough stool accumulates, it may become impacted in the rectum.

Not Drinking Enough Fluid

Low fluid intake can contribute to harder stool, particularly when combined with a low-fibre diet or reduced activity.

Adequate hydration helps stool retain enough moisture to remain easier to pass.

Low Fibre Intake

A diet that is consistently low in fibre may contribute to constipation.

Fruit, vegetables, wholegrains, pulses, nuts and seeds can all help support regular bowel movements. However, if faecal impaction is already present, simply adding a large amount of fibre may not resolve the problem and can sometimes increase bloating or discomfort.

Reduced Physical Activity

Long periods of inactivity can contribute to slower bowel movement.

This is particularly relevant for people who are less mobile because of age, illness, injury or prolonged periods of bed rest.

Regularly Ignoring the Urge to Poo

Repeatedly delaying a bowel movement can allow stool to remain in the colon for longer.

The longer it stays there, the more water can be absorbed from it, increasing the likelihood of hard stool and constipation.

Medicines

A number of medicines and supplements can contribute to constipation.

These may include:

• Opioid painkillers

• Some iron supplements

• Certain antidepressants

• Anticholinergic medicines

• Some blood pressure medicines

• Certain calcium-containing medicines or supplements

Do not stop taking prescribed medication without speaking to your GP or pharmacist. If constipation started after a new medicine was introduced, they may be able to suggest an alternative or help manage the side effect.

Pelvic-Floor Problems

Some people have difficulty coordinating the muscles needed to empty the rectum.

If the pelvic-floor muscles do not relax properly during a bowel movement, stool may be difficult to pass even when it has reached the rectum.

This can contribute to repeated straining, incomplete emptying and, over time, stool retention.

Slow Bowel Transit

In some people, stool moves through the colon more slowly than usual.

This gives the bowel more time to absorb water from the stool, making it firmer and more difficult to pass.

Certain Health Conditions

Constipation and faecal impaction can also be associated with conditions that affect bowel movement, mobility, the nervous system or metabolism.

Persistent or recurrent symptoms should therefore not automatically be assumed to be caused by diet alone.

The important point is that overflow diarrhoea is usually a sign of an underlying bowel-emptying problem, rather than simply too much fluid in the stool.

Who Is More Likely to Develop Faecal Impaction?

Faecal impaction can affect anyone, but some people are more likely to develop it because of reduced bowel movement, limited mobility, long-term constipation or medicines that slow the digestive system.

Older Adults

The risk of constipation generally increases with age.

Possible contributing factors include:

• Reduced physical activity

• Lower fluid intake

• Changes in diet

• Multiple medicines

• Reduced bowel motility

• Difficulty getting to or using the toilet

Older adults who are frail or less mobile may be particularly vulnerable to faecal loading and impaction.

People With Reduced Mobility

People who spend long periods sitting or lying down may have slower bowel movement.

This can include those recovering from illness or surgery, people with physical disabilities and those who are largely confined to bed or a chair.

People With Chronic Constipation

Repeated episodes of constipation increase the chance that stool will remain in the rectum for long enough to become hard and difficult to pass.

People who frequently need laxatives or regularly feel that their bowel has not emptied completely may benefit from discussing the underlying cause with a healthcare professional.

People Taking Constipating Medicines

Certain medicines can slow bowel movement or make stool harder.

Opioid painkillers are a particularly well-known cause, but other medicines can also contribute.

If constipation begins after starting a new medicine, speak to your GP or pharmacist rather than stopping prescribed treatment yourself.

People With Neurological Conditions

Conditions affecting the brain, spinal cord or nerves can interfere with the signals and muscle coordination needed for normal bowel emptying.

This can make constipation and stool retention more likely.

People With Pelvic-Floor or Bowel-Emptying Problems

Some people can move stool through the colon normally but have difficulty emptying the rectum effectively.

This may lead to:

• Repeated straining

• A sensation that stool is stuck

• Incomplete emptying

• Frequent unsuccessful trips to the toilet

Over time, retained stool can become increasingly hard.

People Who Regularly Ignore Bowel Urges

Repeatedly delaying a bowel movement gives the colon more time to absorb water from the stool.

This can make stool harder and contribute to a cycle of increasingly difficult bowel movements.

People Who Cannot Easily Recognise or Communicate Symptoms

Faecal impaction may be harder to identify in people who have difficulty recognising, describing or communicating bowel symptoms.

In these situations, changes such as unexpected stool leakage, abdominal discomfort, reduced appetite or changes in normal bowel habits may warrant closer attention.

Recognising these risk factors can be useful because preventing constipation from becoming severe is generally easier than treating faecal impaction once it has developed.

Can You Be Constipated and Have Diarrhoea at the Same Time?

Yes. It is possible to be constipated and still pass loose or watery stool.

This can happen when a large amount of hard stool remains in the rectum while softer stool from higher in the bowel passes around it. The result can look like diarrhoea even though the underlying problem is constipation or faecal impaction.

Signs that loose stool may be related to constipation include:

• A recent or ongoing history of constipation

• Hard stools between episodes of loose stool

• Straining to open your bowels

• Passing only small amounts at a time

• A feeling that stool is stuck

• A sensation of incomplete emptying

• Abdominal bloating or discomfort

• Leakage or soiling

This is different from ordinary diarrhoea, where the bowel contents are generally moving through too quickly rather than being held back by retained stool.

The distinction matters because treating only the loose stool may not address the underlying problem. If overflow diarrhoea is caused by faecal impaction, the retained stool needs to be dealt with appropriately.

If loose stools are accompanied by severe abdominal pain, vomiting, significant swelling or an inability to pass wind, seek urgent medical advice.

Should You Take Anti-Diarrhoea Medicine for Overflow Diarrhoea?

Not necessarily.

If diarrhoea is being caused by faecal impaction or retained hard stool, medicines that slow the bowel may not address the underlying problem and could potentially make stool retention worse.

Anti-diarrhoea medicines such as loperamide are designed to reduce bowel movement in certain types of diarrhoea. Overflow diarrhoea is different because the loose stool may be passing around a mass of hard stool that has not been cleared.

Why Treating the Diarrhoea Alone Can Be Misleading

The watery stool is the visible symptom, but the main problem may still be constipation.

If you slow bowel movement without recognising that hard stool is already retained, you may delay appropriate treatment of the impaction.

Signs that loose stool could be related to constipation include:

• Hard stools at other times

• Straining

• Feeling that stool is stuck

• Incomplete emptying

• Abdominal bloating

• Passing only small amounts of stool

• Leakage or soiling

What Should You Do Instead?

If you suspect overflow diarrhoea, particularly if you have been constipated for several days or feel that stool is impacted, speak to a pharmacist or healthcare professional before taking anti-diarrhoea medicine.

Treatment may need to focus on softening and clearing the retained stool rather than slowing the bowel.

Seek urgent medical advice if you also have severe abdominal pain, vomiting, marked swelling or an inability to pass wind.

How Is Faecal Impaction Treated?

Treatment for faecal impaction depends on how much stool has built up, where it is located and how severe the symptoms are.

The aim is to soften and remove the retained stool safely, then reduce the risk of it happening again.

Osmotic Laxatives

Osmotic laxatives help draw or retain water in the bowel, which can soften hard stool and make it easier to pass.

Macrogol, also known as polyethylene glycol, is commonly used for constipation and may also be recommended in higher or structured doses for faecal impaction.

The exact dose and treatment plan can vary, so it is important to follow the instructions provided with the medicine or the advice of a pharmacist or healthcare professional.

Stimulant Laxatives

A stimulant laxative may sometimes be added if an osmotic laxative alone is not enough.

These medicines encourage the muscles of the bowel to contract and move stool towards the rectum.

Examples include:

• Senna

• Bisacodyl

They can cause cramping or urgency in some people.

Suppositories

If stool is lodged low in the rectum, a suppository may sometimes be recommended.

Suppositories are inserted into the rectum and can help stimulate bowel emptying or soften stool, depending on the type used.

Mini-Enemas

A mini-enema introduces a small amount of liquid into the rectum.

This can help soften stool and encourage emptying when the impaction is located close to the rectum.

Removal by a Healthcare Professional

In some cases, impacted stool cannot be cleared adequately with laxatives, suppositories or enemas.

A trained healthcare professional may then need to remove the stool manually.

This is not something to attempt yourself, as doing so can cause injury, bleeding or other complications.

What Happens After the Impaction Is Cleared?

Once the retained stool has been removed, the next step is usually to work out why the impaction developed.

This may involve reviewing:

• Fibre intake

• Fluid intake

• Physical activity

• Toilet habits

• Medicines that can cause constipation

• Pelvic-floor function

• Long-term bowel patterns

Preventing the constipation from returning is important because faecal impaction can recur if the underlying cause is not addressed.

If you have severe abdominal pain, vomiting, significant swelling or cannot pass wind, seek urgent medical attention rather than trying to treat the problem yourself.

Can You Treat Overflow Diarrhoea at Home?

It depends on the cause and severity of the symptoms.

If the loose stool is linked to mild constipation without signs of faecal impaction or bowel obstruction, simple measures at home may help restore more regular bowel movements.

These can include:

• Drinking enough fluid

• Staying gently active

• Responding to the urge to open your bowels

• Using a supportive toilet position

• Taking an appropriate laxative where suitable

• Speaking to a pharmacist if you are unsure which treatment to use

However, overflow diarrhoea can sometimes indicate that hard stool has become impacted in the rectum. In that situation, ordinary home measures may not be enough.

When Home Treatment May Not Be Appropriate

Seek medical advice if you have:

• Persistent watery leakage alongside constipation

• A strong feeling that stool is stuck

• Repeated unsuccessful attempts to open your bowels

• Significant abdominal discomfort or bloating

• Symptoms that do not improve with appropriate self-care

You should seek urgent medical attention if you develop severe abdominal pain, vomiting, marked abdominal swelling or an inability to pass wind.

Avoid Trying to “Flush Out” the Bowel

Drinking excessive amounts of water, suddenly consuming large quantities of fibre or using aggressive bowel cleanses is not an appropriate way to treat suspected faecal impaction.

If retained stool is causing the overflow, treatment may need to focus on softening and clearing the impacted stool with an appropriate laxative, suppository, mini-enema or professional treatment.

The key is to treat the underlying constipation, rather than simply trying to stop the loose stool.

Should You Eat More Fibre if You Have Overflow Diarrhoea?

Fibre can be helpful for preventing and managing uncomplicated constipation, but it is not always the right immediate response when overflow diarrhoea is caused by faecal impaction.

If hard stool is already lodged in the rectum, simply adding more bulk may not clear it and can sometimes increase bloating, pressure or discomfort.

When Fibre Can Help

For people with ordinary constipation, gradually increasing fibre can support more regular bowel movements.

Useful sources include:

• Fruit and vegetables

• Oats and wholegrains

• Beans and pulses

• Nuts and seeds

Fibre is generally most effective when it is increased gradually and combined with adequate fluid intake.

When More Fibre May Not Be Helpful

If you have signs of faecal impaction, such as watery stool leaking around hard stool, repeated unsuccessful attempts to open your bowels or a persistent feeling that stool is stuck, the immediate priority may be to clear the retained stool appropriately.

In this situation, suddenly adding large amounts of bran, fibre supplements or other bulky foods may not solve the problem.

Once the impaction has been treated, fibre can again become an important part of reducing the risk of constipation returning.

Increase Fibre Gradually

A sudden increase in fibre can cause:

• Bloating

• Wind

• Abdominal discomfort

• A feeling of fullness

If your current intake is low, increase fibre gradually rather than making a large change overnight.

If you are unsure whether your symptoms are caused by ordinary constipation or faecal impaction, speak to a pharmacist or healthcare professional before relying on fibre as the main treatment.

When Overflow Diarrhoea Needs Medical Attention

Overflow diarrhoea is not always an emergency, but it can indicate faecal impaction or another bowel problem that needs medical assessment.

Seek medical advice if:

• Loose or watery stool keeps occurring alongside constipation

• You repeatedly feel that stool is stuck

• You are unable to empty your bowel properly

• You regularly need laxatives to pass stool

• Abdominal bloating or discomfort persists

• Your bowel habits have changed without an obvious reason

• Symptoms keep returning after treatment

• You notice blood in your stool or rectal bleeding

• You have unexplained weight loss

You should seek urgent medical attention if overflow diarrhoea is accompanied by:

• Severe or constant abdominal pain

• Vomiting

• Significant or increasing abdominal swelling

• An inability to pass wind

• An inability to pass stool and wind

• Fever

• Rapidly worsening symptoms

These symptoms can occur with bowel obstruction or other conditions that should not be treated at home.

If you are unsure whether loose stool is ordinary diarrhoea or overflow caused by retained stool, a pharmacist or GP can help assess the pattern of symptoms and advise on the most appropriate next step.

How To Prevent Overflow Constipation From Returning

Once faecal impaction or severe constipation has been treated, the next step is reducing the chance of it happening again.

For many people, prevention comes down to keeping stools soft enough to pass comfortably and maintaining regular bowel habits.

Maintain a Consistent Fibre Intake

Fibre can help support regular bowel movements and reduce the risk of stool becoming hard and difficult to pass.

Useful sources include:

• Fruit and vegetables

• Oats and wholegrains

• Beans and pulses

• Nuts and seeds

If your fibre intake is currently low, increase it gradually rather than making a large change all at once.

Stay Adequately Hydrated

Regular fluid intake helps prevent stools from becoming excessively dry.

There is no need to drink excessive amounts of water, but maintaining adequate hydration throughout the day is especially important if you are increasing your fibre intake.

Stay Physically Active

Regular movement can support normal bowel function.

Walking, light exercise and breaking up long periods of sitting may all help, particularly if reduced mobility has contributed to constipation in the past.

Do Not Ignore the Urge to Poo

Repeatedly delaying a bowel movement can allow stool to remain in the colon for longer, where more water may be absorbed from it.

Where possible, respond to the natural urge to open your bowels rather than putting it off.

Establish a Regular Toilet Routine

The bowel often becomes more active after meals, particularly after breakfast.

Giving yourself enough time to use the toilet without rushing can help establish a more regular pattern.

Some people find it useful to try opening their bowels around 15 to 45 minutes after breakfast, when the gastrocolic reflex is naturally more active.

Use a Better Toilet Position

Placing your feet on a small stool so that your knees sit slightly higher than your hips can make bowel emptying easier.

Leaning forwards, relaxing the pelvic floor and avoiding prolonged straining may also help.

Review Medicines That May Be Contributing

If constipation started after beginning a new medicine or supplement, speak to your GP or pharmacist.

Do not stop prescribed medication without advice, but it may sometimes be possible to adjust the treatment or manage the constipation more effectively.

Investigate Recurrent Constipation

If constipation keeps returning despite sensible changes to diet, hydration, activity and toilet habits, it is worth looking more closely at the cause.

Repeated faecal loading or overflow diarrhoea may be linked to:

• Slow bowel transit

• Pelvic-floor dysfunction

• Constipating medicines

• Reduced mobility

• Long-term bowel conditions

Recurring symptoms should not simply be managed indefinitely with short-term remedies. A GP or pharmacist can help assess whether further investigation or a longer-term bowel management plan is needed.

Where Magnesium Fits Into Constipation Management

Certain forms of magnesium can affect bowel movements because they have an osmotic effect, meaning they help retain water within the bowel.

This can soften stool and make it easier to pass, which is why some magnesium compounds are used in products intended to support bowel regularity.

How Magnesium Can Affect Stool Consistency

When more water remains in the intestinal contents, stool can become softer and easier to move through the bowel.

Depending on the form and dose, magnesium may therefore:

• Help soften hard stools

• Make bowel movements easier to pass

• Support more regular bowel movements in some people

Different forms of magnesium are not interchangeable, however, because they can behave differently in the digestive system.

Magnesium Hydroxide

Magnesium hydroxide is one of the forms most commonly associated with a laxative effect.

It works by increasing the amount of water retained in the bowel, which can help soften stool and encourage bowel emptying.

Magnesium Citrate and Other Forms

Magnesium citrate can also have an osmotic effect and is sometimes used for constipation.

Other forms, such as magnesium glycinate, are generally selected for different reasons and are less commonly used where an effect on bowel movements is the main objective.

Magnesium Is Not Appropriate for Everyone

Magnesium-containing laxatives or supplements may not be suitable for everyone, particularly people with impaired kidney function or certain other medical conditions.

Possible side effects can include:

• Loose stools

• Diarrhoea

• Abdominal cramping

• Nausea

If you regularly need magnesium or other laxatives to open your bowels, speak to a GP or pharmacist rather than relying on repeated self-treatment.

Magnesium should also not be used as a substitute for appropriate treatment where faecal impaction or bowel obstruction is suspected.

Where OxyTech May Fit

OxyTech is a food supplement that contains magnesium hydroxide, alongside vitamin C and citrus bioflavonoids.

Because magnesium hydroxide can help retain water within the bowel, OxyTech may be relevant for people considering a magnesium-containing supplement as part of their wider bowel-health routine.

Each OxyTech tablet contains:

• Magnesium Hydroxide 190mg

• Vitamin C 75mg

• Sodium 25mg

• Citrus Bioflavonoids 25mg

OxyTech should not be viewed as a treatment for faecal impaction, overflow diarrhoea caused by impacted stool or bowel obstruction.

If you suspect that hard stool is impacted, particularly if you have persistent overflow diarrhoea, abdominal pain, vomiting, marked bloating or difficulty passing wind, medical assessment is more appropriate than relying on a supplement.

For people dealing with occasional constipation, it is also important to consider the wider factors that support normal bowel function, including adequate fluid intake, appropriate fibre intake, regular movement, good toilet habits and responding to the natural urge to open the bowels.

When To Speak to Your GP or Pharmacist

Overflow diarrhoea can sometimes improve once the underlying constipation is treated, but persistent or recurring symptoms should not be ignored.

Speak to your GP or pharmacist if:

• Loose or watery stool keeps occurring alongside constipation

• You repeatedly feel that stool is stuck

• You regularly experience incomplete bowel emptying

• Constipation keeps returning

• You frequently need laxatives to open your bowels

• Your bowel habits have changed without an obvious reason

• You have ongoing abdominal discomfort or bloating

• You notice rectal bleeding or blood in your stool

• You have unexplained weight loss

• You think a medicine or supplement may be contributing to constipation

A pharmacist can advise on suitable short-term treatments and whether a particular laxative may be appropriate.

Your GP may recommend further assessment if symptoms are persistent, recurrent or suggest that the problem is more than uncomplicated constipation.

Seek urgent medical attention if you develop severe abdominal pain, vomiting, marked abdominal swelling, fever or an inability to pass stool or wind, as these symptoms can indicate bowel obstruction or another condition requiring prompt assessment.