Magnesium is a naturally occurring mineral in your body that supports its normal function. Magnesium occurs in different forms, such as:
- Magnesium nitrate (Mg(NO3)2)
- Magnesium sulfate (MgSO4)
- Magnesium oxide
- Magnesium hydroxide
Like some other elements, it has healing effects on cattle skin diseases, which was first discovered when cattle consumed well water containing magnesium.1
MgSO4 is also known as Epsom salts and has been used in the treatment of constipation in different parts of the world, including China, Japan, and the West for over 250 years.
In Europe, the different forms of magnesium are used as laxatives i.e. they help people to open the bowel, particularly in case of patients with constipation.
Magnesium is one of the most abundant cations in the body and serves as a cofactor for more than 500 enzymes2.
The positive effects of magnesium salts in constipation relief have been reported in several studies.3, 4
How does magnesium affect bowel movements?
Magnesium can be classified as an osmotic laxative, which is different from stimulant laxatives. The acid within the stomach triggers a cascade of reactions by converting magnesium oxide to magnesium chloride.
The formed magnesium chloride is then converted to magnesium bicarbonate through the effect of sodium hydrogen carbonate (NAHCO3), which is a pancreatic secretion released into the duodenum, which is part of the small intestine.
The final product that acts on the intestine is magnesium carbonate. Magnesium hydrogen carbonate and magnesium carbonate act by increasing the osmotic pressure of the intestinal lumen. In essence, they increase the amount of salt inside the intestine, which leads to the movement of water from tissue cells into the intestinal lumen.
The effect of this is the increase in water content and volume of stool. The water influx makes the stool swell, resulting in stimulation of the intestinal wall and the movement or motor activity of the intestinal wall.5 This results in pressure to open the bowel; hence, its usefulness in constipation relief or treatment of constipation.
Magnesium also forms citrate or sulfate salts, which promote fluid retention within the digestive tract.
This fluid retention indirectly alters the movement of the bowel, making these salts act as laxatives. Research has shown an association between magnesium intake and constipation.
Low magnesium intake is associated with the prevalence of constipation. This suggests that the role of magnesium in intestinal motility may help prevent constipation, not just treat the condition.6
Which magnesium is best for bowel movements?
There are different forms of magnesium doing different things in the body. However, for a bowel movement and treatment of constipation, magnesium oxide appears to be the best.7
This is referred to as milk of magnesia. When this form is taken with water whether as a magnesium supplement, as a tablet or as a soluble form in a sachet, it forms magnesium hydroxide, which helps to relieve constipation and improve bowel movement.
Magnesium citrate (magnesium with citrate) is very useful in stool cleaning or bowel evacuation prior to interventions, such as radiological examination, surgery, or endoscopy. The use of magnesium sulfate as a laxative in patients with cerebral palsy has been reported.8
How much magnesium should I take for bowel movements?
Magnesium is administered by mouth (orally). The dosage varies depending on the age of the individual and the form of magnesium. Ideally, a maximum of 2 grams (2000 milligrams) of magnesium oxide should be taken within 24 hours. It should be taken before or after meals three times a day or taken once a day before bedtime.5 Based on the prescribed dosage, which should be taken orally, the following guidelines should be followed.
For children between the ages of 3 and 11, 5 to 10 ml is to be administered with water at bedtime. For children between 12 and 17, 30-45 ml should be administered with water at bedtime.
For adults, 30 to 45 ml is administered with water at bedtime.9
For magnesium citrate in sachet form, this should be taken orally. A sachet should be taken early in the morning and then a sachet after six to eight hours.10
The dosage varies from 250 mg to 2 g depending on the severity of the constipation. However, a dosage of 2 g may result in hypermagnesemia if there is no immediate response.
Magnesium sulfate can be taken as an oral dietary supplement at 4% concentration to make a dose of 65 mg/day for children aged 1-3 years. It can also be given at a dose of 110 mg/day and 350 mg/day for children aged 3-8 years and above 9 years respectively.8
Side effects and other concerns
There are various side effects and concerns associated with the usage of magnesium. Some of the common side effects are headache, nausea, and gastrointestinal discomfort.
Some of the uncommon side effects include seizures, adverse skin reactions, vomiting, confusion, gastrointestinal disorders, and electrolyte imbalance.
Due to the mode of action of magnesium oxide, including antacid and adsorptive actions, magnesium may interact with the absorption and excretion of other drugs. Magnesium may interact with bisphosphonates, tetracycline, and new quinolones thus diminishing their effect. These drugs must not be taken together, and adequate time must be left between dosing when the drugs are prescribed together.5
Magnesium also diminishes the effects of iron supplements fexofenadine, digitalis, and polycarbophil calcium. The inhibitory effect of magnesium on the efficacy of the following drugs has been reported; azithromycin, celecoxib, gabapentin, mycophenolate mofetil, and penicillamine. Magnesium oxide increases the ability of the kidney to increase a lot of calcium. In addition, the use of proton pump inhibitors (PPI) and H2 receptor antagonists reduces the laxative effects of magnesium oxide.5
Magnesium sulfate reduces the ability of the intestine to absorb carbohydrates, fat, and protein following consumption of solid food.8
Magnesium oxide is relatively safe because of its poor bioavailability; however, this may induce hypermagnesemia.11 The magnesium levels in the blood are regulated by the kidney, with the normal range between 1.8- 2.4 mg/dL and 3.0 mg/dL. Any value above the normal range is termed hypermagnesemia. Interaction between activated vitamin D and magnesium can lead to hypermagnesemia because this can lead to increased absorption and reabsorption of magnesium from renal tubules.12
Hypermagnesemia can manifest as headache, nausea, cutaneous flushing, and light-headedness. Magnesium levels in blood greater than 5.0 mg/dL can result in complete heart blockage, respiratory failure, and cardiac arrest.13
Magnesium is a naturally occurring element and has a lot of use in humans. One of the uses is to help bowel movement or for constipation relief. Magnesium occurs in various forms and some of these forms are useful for inducing bowel movement. Despite the usefulness of various forms of magnesium, care must be taken to prevent drug interaction and reduce side effects.
- Rudolf RD. The use of Epsom salts, is historically considered. Can Med Assoc J. 1917;7(12):1069-71.
- de Baaij JH, Hoenderop JG, Bindels RJ. Magnesium in man: implications for health and disease. Physiol Rev. 2015;95(1):1-46.
- Naumann J, Sadaghiani C, Alt F, Huber R. Effects of Sulfate-Rich Mineral Water on Functional Constipation: A Double-Blind, Randomized, Placebo-Controlled Study. Forsch Komplementmed. 2016;23(6):356-63.
- Bothe G, Coh A, Auinger A. Efficacy and safety of a natural mineral water rich in magnesium and sulphate for bowel function: a double-blind, randomized, placebo-controlled study. Eur J Nutr. 2017;56(2):491-9.
- Mori H, Tack J, Suzuki H. Magnesium Oxide in Constipation. Nutrients. 2021;13(2).
- Murakami K, Sasaki S, Okubo H, Takahashi Y, Hosoi Y, Itabashi M, et al. Association between dietary fiber, water and magnesium intake and functional constipation among young Japanese women. European Journal of Clinical Nutrition. 2007;61(5):616-22.
- Mori S, Tomita T, Fujimura K, Asano H, Ogawa T, Yamasaki T, et al. A Randomized Double-blind Placebo-controlled Trial on the Effect of Magnesium Oxide in Patients With Chronic Constipation. J Neurogastroenterol Motil. 2019;25(4):563-75.
- National Institute for Health (NIH). Effect of Oral Magnesium Therapy on Constipation on Cerebral Palsy Children 2018 [Available from: https://clinicaltrials.gov/ct2/show/NCT03471312.
- National Institute for Health and Care Excellence (NICE). Magnesium Hydroxide 2023 [Available from: https://bnf.nice.org.uk/drugs/magnesium-hydroxide/.
- National Institute for Health and Care Excellence (NICE). Magnesium citrate with sodium picosulfate 2023 [Available from: https://bnf.nice.org.uk/drugs/magnesium-citrate-with-sodium-picosulfate/.
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnes Res. 2001;14(4):257-62.
- Mori H, Suzuki H, Hirai Y, Okuzawa A, Kayashima A, Kubosawa Y, et al. Clinical features of hypermagnesemia in patients with functional constipation taking daily magnesium oxide. J Clin Biochem Nutr. 2019;65(1):76-81.
- Khairi T, Amer S, Spitalewitz S, Alasadi L. Severe Symptomatic Hypermagnesemia Associated with Over-the-Counter Laxatives in a Patient with Renal Failure and Sigmoid Volvulus. Case Rep Nephrol. 2014;2014:560746.