Milk of magnesia can provide quick relief from constipation by drawing water from the body into the bowels, which softens the stool. It can start working within 30 minutes to 6 hours.

Milk of magnesia (magnesium hydroxide) is a popular over-the-counter (OTC) medication for constipation.

Constipation is a common gastrointestinal issue that many people experience at some point. Whether due to dietary factors, lifestyle choices, or other underlying causes, it can cause discomfort and inconvenience.

This article examines how milk of magnesia relieves constipation, how people can use it, and other treatment options.

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Milk of magnesia is an osmotic laxative. The United Kingdom’s National Health Service (NHS) states that osmotic laxatives draw water from the body into the bowel. This helps to soften the stool, making it easier to pass.

When a person ingests it, the magnesium ions in the solution are inadequately absorbed in the intestines. This causes the intestines to take in water from surrounding tissues, increasing the fluid content in the bowels.

The increased fluid content in the intestines helps soften and break down the stool. This makes it less hard and compacted, which is particularly helpful for people with constipation who often have dry and hard stools.

Magnesium can increase the movement and contractions of the bowel muscles, known as peristalsis. As a result, the stool is propelled through the intestines more efficiently.

It is important for people to always follow the instructions provided on the product label or as directed by a doctor.

It is usually preferable for individuals to take milk of magnesia before bedtime unless a healthcare professional says otherwise.

Before using, a person will need to shake the bottle well and then use the measuring spoon or cup provided to measure the correct dosage.

Dosage recommendations may vary depending on the specific brand and formulation. The dose can also vary depending on someone’s age:

Adults and children ages 12 years and over2–4 tablespoons (tbsp), or 30–60 milliliters (ml)
Children ages 6–11 years1–2 tbsp, or 15–30 ml

Parents, caregivers, and guardians should speak with a doctor before giving milk of magnesia to children under the age of 6 years.

It is important a person does not exceed 60 ml in 24 hours.

How long does it take to work?

Milk of magnesia typically works relatively quickly, often within 30 minutes to 6 hours after ingestion. This makes it an effective choice for individuals seeking fast relief from constipation.

Milk of magnesia is not suitable for people:

There is insufficient evidence about the use during pregnancy or when nursing. Pregnant people should only use milk of magnesia under the supervision of a doctor.

Some medications can interact with milk of magnesia. It is important for people to consult a doctor if they take other medications, especially if they are unsure about potential interactions.

Some other options to help alleviate constipation include:

  • Fiber supplements: Those such as psyllium husk or methylcellulose can help bulk up the stool and promote regular bowel movements. People need to drink plenty of water when using fiber supplements.
  • Stool softeners: Options such as docusate sodium add moisture to the stool, making it easier to pass. They are generally safe for short-term use.
  • Prescription drugs: If OTC options are ineffective, a doctor may prescribe stronger medications, such as prescription-strength laxatives or prokinetic agents.
  • Probiotics: Some people find relief from constipation by taking probiotics, which can help improve the balance of gut bacteria and promote regular bowel movements.
  • Traditional remedies: Herbal teas, prunes, or prune juice can have mild laxative effects.

There are many ways people can help reduce the likelihood of developing constipation. These include:

  • increasing fiber intake by eating more fruits, vegetables, whole grains, and legumes
  • drinking plenty of water throughout the day to stay hydrated
  • engaging in regular physical activity to help stimulate bowel movements
  • establishing a regular bathroom routine, such as going at the same time each day
  • avoiding delaying or ignoring the urge to have a bowel movement

People should contact a doctor if they experience constipation lasting more than 2 weeks, especially if it does not improve with OTC remedies and lifestyle changes.

Chronic constipation can be a symptom of an underlying medical condition that requires evaluation and treatment.

Other indications that someone should speak to a doctor include:

Read on for some commonly asked questions and answers about milk of magnesia for constipation.

Can milk of magnesia cause diarrhea?

Using laxatives, such as milk of magnesia, for too long or too often can result in diarrhea. Excessive or prolonged diarrhea can lead to dehydration.

It is important for a person to drink plenty of fluids while using this medication.

Is milk of magnesia better than a laxative?

Milk of magnesia is a type of laxative, specifically an osmotic laxative.

When comparing it to other types of laxatives, the choice depends on various factors, including an individual’s specific needs, preferences, and any underlying medical conditions.

How long does it take to wear off?

People usually experience a bowel movement soon after taking milk of magnesia. This means someone can expect relief from constipation within a few hours. It typically does not cause long-term effects.

Milk of magnesia is a popular OTC medication to help relieve constipation. It works by drawing water from the body into the bowel. This can soften the stool, making it easier to pass.

People should always speak with a doctor before trying new medications, especially if they are already taking other types.