By Matt Gowan, BSC, ND
July 8, 2017


Natural Laxatives – Bulk, Osmotic and Stimulating laxatives

By Matt Gowan, BSC, ND
July 8, 2017

Natural laxatives are substances that help promote a bowel movement. They are typically derived from plants or mineral sources. Four main classes of natural laxatives (bulk, osmotic and stimulating laxatives plus bowel lubricants) exists. Each class works by different mechanisms with each natural laxatives having advantages and disadvantages. Understanding how they work will help choose the best one for you.


Bulk Laxatives are substances that absorb water and expand in the bowels. Plants rich in fiber and mucilage are used as bulk laxatives. Bulk laxatives are found to be effective in the treatment of constipation.1–3 They improve the consistency and frequency of bowel movements by reducing colonic transit time.4–8 In addition, they also alleviate clinical symptoms of constipation including bloating and straining and pain on defacation.6,9

How do bulk laxatives work?

Fiber acts like a sponge; it absorbs water and expands. Thus bulk laxatives hydrate and lubricate the stool and make it softer and easier to pass. Also, because fiber adds volume to the stool it expands and stimulates “stretch receptors” in the lumen of the bowels to promotes peristalsis. This produces synchronized contraction and relaxation of the intestines to move the stool along.

Ideally, your diet should be rich in fruits and vegetables that are high in fiber. However, in some cases the diet alone may not adequately provide sufficient fiber and supplementing with a bulk laxative may be required.

  • Psyllium husk or Ispaghula (Plantago spp.)
  • Flaxseeds (Linum usitatissimum)
  • Chia seeds (Salvia hispanica)
  • Slippery elm (Ulmus rubra)

Psyllium – Bulk Laxatives

Are bulk laxatives safe?

In general, bulk laxatives are considered safe, but certain precautions should be taken:

  1. Drink lots of water. Bulk laxatives need lots of water to expand. If inadequate water is consumed, they can cause blockages.
  2. Avoid taking when severely constipated.  I would not recommend taking a bulk laxative if you have not had a bowel movement for 2-3 days. The extra fiber can make the bloating and gas worse. Instead, take an osmotic or stimulating laxative to induce a bowel movement and then take a bulk laxative to maintain regularity.
  3. Rule-out intestinal blockage. In rare cases, a twisting of the bowel or obstruction of the bowel can occur. This is a serious condition and should be rule-out before taking any laxatives. Consult your healthcare provider.
  4. Esophageal obstruction has occurred in some patients taking psyllium.  Psyllium husk getting stuck in the esophagus and then expanding is a choking risk. This can be avoided by taking sufficient water and taking psyllium powder rather than granules.10
  5. Avoid taking medication with a bulk laxative. Bulk laxatives can reduce the absorption of certain medications. Take medications a few hours away from any bulk laxative.


Dietary oils act can help maintain regularity. Olive oil and other oils have been used as home remedies for constipation for centuries, and some research supports their traditional use. A recent study with hospitalized patients showed that both olive oil and flaxseed oil improved bowel function compared to the standard treatment.11   Some examples of bowel lubricants:

Some examples of bowel lubricants:

  • Olive oil
  • Flaxseed oil
  • Mineral oil

Aside: Many of my patients report an improvement in bowel movements with fish oil supplementation, but no studies exist. Presumaworkfish oils works by the same mechanism as the above oils.

How do bowel lubricants work as natural laxatives?

When the consumption of oil exceeds the body’s ability to absorb it, the oil remains in the intestines. This lubricates the stool making it easier to pass. Furthermore, consumption of oil causes the release of bile that stimulates peristalsis.12

How do I take a bowel lubricant?

Try taking one tsp of olive or flaxseed oil. Increase if required.

How safe are bowel lubricants?

Olive, flaxseed and fish oils are very safe and have additional benefits on the cardiovascular system. In general, high-fat meals can cause minor gastrointestinal discomfort, including cramping and diarrhea but are otherwise safe.

Caution: Patients with gallstones should be careful consuming large amounts of oil because it could precipitate a gall bladder attack.


Osmotic laxatives pull water into the bowels to help moisten the stool and promote a bowel movement. Magnesium citrate is my preferred natural laxative to help with both acute and chronic constipation and other examples include:

  • Magnesium citrate
  • Magnesium glycinate
  • Magnesium oxide
  • Vitamin C
  • Sorbitol
  • Lactulose

How do Osmotic laxatives work?

Osmotic laxatives create a “hypertonic” solution in the bowels that causes an influx of water. This pulls water into the bowels making them moist and malleable and therefore easier to pass.

Magnesium is an essential mineral that has many functions in the body. It helps relax muscles and has a calming effect on the nervous system. Several forms of magnesium can be used as a natural laxative including magnesium citrate, magnesium glycinate and magnesium oxide (i.e. milk of magnesia). Magnesium citrate is one of the most commonly used purgative13,14Magnesium citrate alone or with other laxatives is often used for bowel preparation during colonoscopy.15 Milk of magnesia was found to be effective in treating constipation, especially among children.16,17 It increases the frequency of bowel movement18 and reduces solid stool.19

Are osmotic laxatives safe?

The use of magnesium citrate was found to be well-tolerated and less frequent adverse events were observed compared to other laxatives.20,21 However, high amounts of osmotic laxatives will produce loose stools and even diarrhea with associated cramping pain.  Some additional issues:

  1. Do not overdose! Very high doses of milk of magnesia can lead to hypermagnesemia, with symptoms including low pressure, confusion, and heart problems. 22
  2. Drink lots of water. Because osmotic laxatives pull water from the body into the stool, they can cause dehydration.


Stimulating laxatives directly act on the intestines to stimulate bowel movements. They are typically divided into two main classes.  Anthraquinones herbs (e.g. Senna) and castor oil.

A. Senna and other anthraquinone containing herbs

The senna plant (Senna alexandrina or Cassia Officinalis) is the most famous natural laxative and its use in herbal medicine dates back to the Ancient Egyptian.  Medical doctors still recommend drugs extracted from the senna plant for acute constipation. Taken orally it produces a bowel movement within 6-12 hours.13  Senna was found to be effective in treating constipation among the elderly23–26, children27, and adults.28 It also improves constipation after surgery,28 chemotherapy29 and due to certain medications.30

Senna -Natural Laxative

Senna – Stimulating Laxative

Although Senna is the most popular stimulating laxative other anthraquinone containing herbs are used in herbal medicine including:

  • Aloe resin (Aloe spp.)
  • Buckthorn (Rhamnus frangulis; Rhamnus purshiana)
  • Rhubarb (Rheum palmatum)
  • Yellow dock (Rumex crispus)

How do anthraquinones work as natural laxatives?

Anthraquinone glycosides are the active ingredient in the above stimulating laxatives. Bacteria in the large intestine remove the sugar component and release the anthraquinone. These compounds stimulate the nerves of the intestines (myenteric plexus) to promote peristalsis and an influx of water.31 Defecation usually occurs within 6-8 hrs.

Are stimulating laxatives safe?

It is unlikely that stimulating laxatives are harmful when taken at the recommended dose.32 However there are several precautions that should be noted.

  1. Avoid long-term use. Some sources state that taking anthraquinone glycosides for greater than 7-10 days may cause dependence. When possible only use them only acutely.
  2. Avoid high doses. Taking large amounts of anthraquinone glycosides can cause cramping pains and diarrhea.
  3. Chronic use of senna leads to a characteristic brown pigmentation of the colon. There are some concerns that these agents are carcinogenic, but some studies do not suggest a relationship with colorectal cancer.13
  4. Pregnant women might be able to use senna but talk to your doctor. Senna does not cause congenital abnormalities among pregnant women with constipation.33

Aside: Recent research suggests that long-term use of these agents is probably safe and may be necessary among persons with cognitive impairment and bedridden patients.13

B. Castor oil

Castor oil is a clear, thick sticky oil extracted from castor beans (Ricinus communis). It has been used for thousands of years as a stimulant laxative in both eastern and western medicine.   Its active ingredient is a fatty acid called ricinoleic acid that works by a slightly different mechanism than the anthraquinone glycoside.  Castor oil acts much quicker than anthraquinone laxatives and has been used in poisonings.

In addition to its internal use, Castor oil may be used topically for constipation.  Topical application of castor oil produces gentler laxative effects than taking it internally. Castor oil packs infused with the oil topically to the abdomen decreases the symptoms of constipation.34

Natural Laxatives - Stimulating Laxatives - Castor oil

Castor Plant – Source of Castor Oil

How does castor oil work as a natural laxative?

Castor oil contains ricinoleic acid a type of fatty acid. Ricinoleic acid acts as irritant inducing peristalsis starting in the small intestine (compared to anthraquinones that start working in the large intestine). It significantly increases the transit time of the bowels producing watery stool within 3-5 hours. Ricinoleic acid flushes out both the small and large intestines thus impairing the absorption of bowel contents.  This will impede the absorption of nutrients but also reduce absorption of toxins in the case of overdose or poisoning.

How safe is castor oil?

External use of castor oil has no significant side-effects.  Internal use of castor oil is generally recognized as safe and effective for use as a stimulant laxative.35 However, castor oil is not my first choice as a natural laxative. Long-term use can cause malabsorption, gut inflammation, abdominal pain and nausea.36–38 Moreover, chronic use may lead to dehydration and loss of electrolytes especially potassium. Potassium deficiency may cause heart and muscle problems.

Caution: Castor oil should be avoided in pregnant women.  Historically it has been used to induce labour and may increase the risk of miscarriage because it acts on the uterine muscles.39

WARNING: DO NOT EAT CASTOR BEANS. WHOLE CASTOR BEANS ARE HIGHLY TOXIC. Castor beans contain a highly toxic compound called ricin that inhibits cell replication.  Ricin is water soluble and thus is not found in castor oil. Ingesting even small amounts of ricin can cause death.

Summary of Natural Laxatives

Several different classes of natural laxatives exist.  Bulk laxatives (e.g. psyllium, flax seeds) are rich in fiber and best suited for stimulating sluggish bowels and helping to maintain regularity.  In severely constipated people it is best to induce a bowel movement using an osmotic laxative (e.g. magnesium citrate) or stimulating laxative (e.g. senna) rather than take a bulk laxative.  Once acute constipation has resolved the bulk laxatives can then be reintroduced.  Long-term use of stimulating laxatives is generally not recommended unless absolutely required.  Taking bulk laxatives (e.g. flaxseeds, chia), bowel lubricants (e.g. olive olive, fish oil, flaxseed oil) and osmotic laxatives (e.g. magnesium) can safely be consumed long-term without serious side-effects.  If you suffer from chronic constipation seek help from a naturopathic doctor who can help you determine food

If you suffer from chronic constipation seek help from a naturopathic doctor who can help you determine food sensitivities that may contribute to your constipation.

Author & Photographer: Matt Gowan, BSc, ND
All images are copyright of Matt Gowan ©2017

Disclaimer: This content is subject to change. The information is intended to inform and educate; it does not replace the medical evaluation, advice, diagnosis or treatment by a healthcare professional. © 2017 NDAssist Inc. and/or its affiliates. All rights reserved.

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