thumb|Glycerin suppositories used as laxatives.
Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation.
Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and bowel examinations, and may be supplemented by enemas under certain circumstances. Sufficiently high doses of laxatives may cause diarrhea. Some laxatives combine more than one active ingredient, and may be administered orally or rectally.
Types
Bulk-forming agents
Bulk-forming laxatives, also known as roughage, are substances, such as fiber in food and hydrophilic agents in over-the-counter drugs, that add bulk and water to stools so they can pass more easily through the intestines (lower part of the digestive tract).
Properties
- Site of action: small and large intestines
- Onset of action: 12–72 hours
- Examples: dietary fiber, Metamucil, Citrucel, FiberCon
Bulk-forming agents generally have the gentlest of effects among laxatives,
- Fruits, such as bananas, though this depends on their ripeness, kiwifruits, prunes, apples (with skin), pears (with skin), and raspberries
Properties
- Site of action: colon
- Onset of action: 6–8 hours
- Example: mineral oil Mineral oil may decrease the absorption of fat-soluble vitamins and some minerals. They also stimulate peristaltic action and can be dangerous under certain circumstances.
thumb|Senna plant
Properties
- Site of action: colon
- Onset of action: 6–10 hours
- Examples: senna, bisacodyl
Miscellaneous
Castor oil is a glyceride that is hydrolyzed by pancreatic lipase to ricinoleic acid, which produces laxative action by an unknown mechanism.
Properties
- Site of action: colon, small intestine (see below)
- Onset of action: 2–6 hours
- Examples: castor oil
Prucalopride (brand name Resolor) is a current drug approved for use in the EU since October 15, 2009, in Canada (brand name Resotran) since December 7, 2011, and in the United States since December 2018.
Chloride channel activators
Lubiprostone is used in the management of chronic idiopathic constipation and irritable bowel syndrome. It causes the intestines to produce a chloride-rich fluid secretion that softens the stool, increases motility, and promotes spontaneous bowel movements.
Comparison of available agents
{| class="wikitable sortable" border="1"
|+Common stimulant laxatives
|-
! Preparation(s) !! Type !! Site of action !! Onset of action
|-
| Cascara (casanthranol)|| Anthraquinone || colon || <span style="display:none">3</span>6–8 hours
|-
| Buckthorn || Anthraquinone || colon || <span style="display:none">3</span>6–8 hours
|-
| Senna extract (senna glycoside) || Anthraquinone || colon || <span style="display:none">3</span>6–8 hours
|-
| Aloe vera (aloin) || Anthraquinone || colon || <span style="display:none">5</span>8–10 hours
|-
| Phenolphthalein || Triphenylmethane || colon || <span style="display:none">4</span>8 hours
|-
| Bisacodyl (oral) || Triphenylmethane || colon || <span style="display:none">6</span>6–12 hours
|-
| Bisacodyl (suppository) || Triphenylmethane || colon || <span style="display:none">1</span>60 minutes
|-
| Castor oil || Ricinoleic acid || small intestine || <span style="display:none">2</span>2–6 hours
|}
Effectiveness
For adults, a randomized controlled trial found PEG (MiraLax or GlycoLax) 17 grams once per day to be superior to tegaserod at 6 mg twice per day. A randomized controlled trial found greater improvement from two sachets (26 g) of PEG versus two sachets (20 g) of lactulose. 17 g per day of PEG has been effective and safe in a randomized, controlled trial for six months. Another randomized, controlled trial found no difference between sorbitol and lactulose.
For children, PEG was found to be more effective than lactulose.
Problems with use
Laxative abuse
Some of the less significant adverse effects of laxative abuse include dehydration (which causes tremors, weakness, fainting, blurred vision, kidney damage), low blood pressure, fast heart rate, postural dizziness and fainting; kidney failure, factitious diarrhea and other problems. The colon will need more quantities of laxatives to keep functioning, this will result in a lazy colon, infections, irritable bowel syndrome, and potential liver damage.
Although some patients with eating disorders such as anorexia nervosa and bulimia nervosa abuse laxatives in an attempt to lose weight, laxatives act to speed up the transit of feces through the large intestine, which occurs after the absorption of nutrients in the small intestine is already complete. Thus, studies of laxative abuse have found that effects on body weight reflect primarily temporary losses of body water rather than energy (calorie) loss.
Laxative gut
Physicians warn against the chronic use of stimulant laxatives due to concern that chronic use could cause the colonic tissues to get worn out over time and not be able to expel feces due to long-term overstimulation. A common finding in patients having used stimulant laxatives is a brown pigment deposited in the intestinal tissue, known as melanosis coli.
Historical and health fraud uses
Laxatives, once called "physicks" or "purgatives", were used extensively in historic medicine to treat many conditions for which they are now generally regarded as ineffective in evidence-based medicine. Likewise, laxatives (often termed colon cleanses) may be promoted in alternative medicine for various conditions of quackery, such as "mucoid plaque".
See also
- ATC code A06
- Bowel management
- Cathartic
- Dietary fiber
- Diuretic
- Maltitol
- Enema
- Suppository
- Transanal irrigation