Dealing with constipation can be frustrating and uncomfortable. Thankfully, several options can help treat constipation, e.g., the use of laxatives.
Laxatives come in many forms, including bulk-forming laxatives, stool softeners, lubricants, and osmotic agents.
Magnesium-based laxatives are in the class of saline osmotic laxatives, which work by drawing water into the bowels to trigger bowel movements.
Magnesium-based laxatives are not intended for long-term use, but when used safely and correctly, they can help relieve constipation in the short term.
In this article, I’ll explain magnesium’s role in the body, how magnesium supplements help relieve constipation, and which side effects and safety recommendations to know before taking magnesium-based laxatives.
Finally, I’ll cover when it’s important to seek advice or treatment from a healthcare professional.
What Magnesium Does to the Body
Magnesium is an important mineral that’s naturally present in the human body. It helps maintain organ functioning, especially the kidneys, heart, and muscles.
It also plays an important role in the processes that regulate nerve impulse conduction, muscle contraction, and normal heart rhythm.
An adult body contains around 25g of magnesium. 50-60% of this mineral is in the bones, while the rest can be found in soft tissues.
Magnesium can also be obtained by eating certain foods, like green leafy vegetables, nuts, and whole grains.
In general, foods containing high levels of dietary fiber are good sources of magnesium.
Most people can maintain adequate magnesium levels on their own, but certain disorders, like irritable bowel syndrome (IBS), can lower the body’s magnesium levels.
Magnesium and Poop
Magnesium can also be taken as a laxative to help relieve constipation. Magnesium-based laxatives belong to a class of laxatives called saline osmotics.
They work by drawing water into the bowels to trigger bowel movements and make them easier to pass.
There are different kinds of magnesium-based laxatives, including magnesium citrate, magnesium hydroxide, or magnesium oxide (milk of magnesia).
The active ingredients in these products can include magnesium, sulfate, citrate, and phosphate.
Causes of Constipation
Constipation is the difficulty to pass easy and frequent bowel movements.
Typically, being constipated means that you have fewer than three bowel movements a week.
Chronic constipation describes when you’ve had difficulty passing bowel movements for several weeks or longer.
There are several possible causes of constipation.
One common cause of constipation is called “functional constipation,” when waste moves too slowly through the colon, making fecal matter harder to pass.
Additional possible causes of constipation include:
- Bowel stricture or obstruction: When there is a narrowing of the colon or blockage in the intestines.
- Anal fissures: Fissures are tiny tears in the thin, moist tissue that lines the anus, which can bleed when irritated, causing constipation, pain, and bloody stools.
- Rectocele: When the rectum bulges through the back wall of the vagina.
- Nerve problems: Some neurological conditions, including multiple sclerosis (MS), stroke, and Parkinson’s disease, can affect the nerves and muscles in the rectum and colon that manage bowel movements.
- Pelvic muscle problems: Weakened pelvic muscles, anismus (the inability to relax pelvic muscles to have a bowel movement), or dyssynergia (when pelvic muscles don’t properly coordinate contraction and relaxation).
- Dietary factors and issues: Eating certain foods can make constipation worse, including ultra-processed grains, red meat, fried or fast foods, and milk and dairy products and foods generally low in fiber. Dehydration can also cause and worsen constipation.
- Hormonal conditions: Some conditions that affect the balance of hormones in the body can also cause constipation. These conditions include diabetes, overactive parathyroid gland (hyperparathyroidism), pregnancy, and underactive thyroid (hypothyroidism).
- Cancer: Colon, rectal, or abdominal cancer can press on the colon, blocking stool movement.
Any of these conditions call for a doctor’s attention and need to be treated to avoid further complications.
Side Effects and Safety
Taking magnesium-based laxatives may cause side effects.
The most common side effects are loose, watery, or more frequent stools.
However, it’s important to reach out to your doctor as soon as possible if you experience any of the following side effects:
- Blood in stool
- Black, tarry stools
- Slow reflexes
- Severe, persistent stomach pain
- Vomit that looks like coffee grounds
- Inability to have a bowel movement after laxative use
Magnesium-based laxatives are not intended for long-term use. It’s also important not to exceed the amount recommended by your doctor or pharmacist.
Before taking magnesium, be sure to let your healthcare provider know about any existing medical conditions or any medications or supplements you’re currently taking.
Importantly, you should not use magnesium-based laxatives if you have kidney disease.
The standard dose of magnesium will vary depending on the product you’re using and individual factors.
The average dose ranges between 200-500mg, with 2 grams (or 2,000 milligrams) being the maximum dose.
Be sure not to exceed the maximum dose or amount recommended by your doctor or pharmacist.
Alternatives to Magnesium
There are several alternatives to magnesium-based laxatives that may help to relieve your constipation.
Please check with your provider to determine if these are appropriate for your use as certain medical conditions would prohibit the use of some of these alternatives:
- Bulk-forming laxatives: Bulk-forming laxatives are generally safe to use, but they may take anywhere between 12 hours to several days to take effect. Keep in mind that some mild side effects are possible when taking bulk-forming laxatives, such as passing of gas and bloating.
- Stool softeners: These products work by adding moisture to stools to make them softer and easier to pass. Some examples of stool softener brands include Colace, Correctol, and Surfak.
- Lubricants: Mineral oil can be beneficial if you’re experiencing constipation caused by anal fissures or if you’re experiencing pain from hemorrhoids.
- Other osmotics: Other osmotic laxatives are also an option, including those that contain polyethylene glycol (MiraLAX), sodium phosphate (Fleet Phospho-Soda), and sorbitol or lactulose.
Stimulant laxatives are another option for people whose bowel movements are particularly slow. However, physicians usually recommend this option as a last resort only because you can become dependent on them.
When to See a Doctor
Occasional constipation can happen to anyone.
But if you’re experiencing chronic constipation that won’t go away, it’s important to reach out to your doctor for help.
It’s also important to seek immediate medical attention if you notice any severe symptoms, such as bloody or black stool, fever, severe abdominal cramping, or chills.
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Frequently Asked Questions
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.
K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.
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Magnesium Citrate. (2019).
Magnesium Hydroxide. (2019).
Magnesium for Constipation. (2021).