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Overview: Magnesium laxatives are used for occasional constipation. They work by pulling water into your intestines, which makes your poop softer and easier to pass. Diarrhea is a common side effect. Before taking this medicine, talk with your health care provider if you have a sudden change in your ability to poop that lasts for two weeks or longer. Stop taking this medicine and call your health care provider if you see blood in your poop or do not poop after taking it. Magnesium laxatives come in many salts and dosage forms, and you should ask your health care provider if you are not sure which product to take.

Uses

What are magnesium laxatives used for?

Magnesium laxatives are commonly used to relieve occasional constipation.

Magnesium laxatives may also be used for other conditions as determined by your health care provider.

How do magnesium laxatives work (mechanism of action)?

Constipation is a common condition where you have fewer bowel movements than normal. You may strain when you poop and have hard stools, bloating, or cramps. Magnesium laxatives are a type of laxative known as an osmotic laxative or saline laxative. They work by pulling water into your intestines. This helps soften poop and makes it easier to pass. 

What forms of magnesium are typically used for constipation?

  • Magnesium citrate
  • Magnesium glycinate
  • Magnesium hydroxide (milk of magnesia)
  • Magnesium oxide
  • Magnesium sulfate (Epsom salts)

Some magnesium forms are used as antacids or supplements. See Magnesium Antacids or Magnesium Supplements for more information.

How should I store magnesium laxatives?

Storage requirements may vary among magnesium laxative products. Magnesium laxatives should generally be stored at room temperature, between 68 F and 77 F (20 C and 25 C). Some products may be stored at a temperature between 46 F and 86 F (8 C and 30 C). Avoid excessive heat and freezing. Storage requirements for some magnesium laxatives may not be provided with the product packaging. If you are not sure how to store your magnesium laxative, ask your pharmacist.

Side Effects

What are the most common side effects of magnesium laxatives?

The most common side effects of magnesium laxatives are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Stomach cramps
  • Diarrhea (see below)
  • Nausea
  • Gas

There may be other side effects of magnesium laxatives that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of magnesium laxatives?

While less common, the most serious side effects of magnesium laxatives are described below, along with what to do if they happen.

Severe Allergic Reactions. Magnesium laxatives may cause allergic reactions, which can be serious. Stop taking magnesium laxatives and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching or skin rash
  • Bumps on the skin called hives that can be red, pink, white, or brown, depending on your skin tone
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Diarrhea. Magnesium laxatives may cause diarrhea. Stop taking magnesium laxatives and call your health care provider right away if you have any of the following.

  • Severe diarrhea
  • Diarrhea that does not go away
  • Diarrhea with weakness, dizziness, or fever

Warnings & Precautions

Who should not use magnesium laxatives?

Allergies to Ingredients. People who are allergic to any of the following should not take magnesium laxatives.

  • Magnesium
  • Milk of magnesia (MOM)
  • Any of the ingredients in the specific product 

Your pharmacist can tell you all of the ingredients in the specific magnesium laxative products they stock.

What should I know about magnesium laxatives before using them?

Magnesium laxatives come in many different salts and dosage forms. Some may work better for you than others. Some may cause fewer side effects than others. If you are not sure which magnesium laxative product you should take, ask your pharmacist or other health care provider.

Read and follow the instructions for the product you have and make sure you understand how to take it properly. The dose listed on the product label is usually a 24-hour dose. Depending on the product, the dose may be taken all at once or divided into smaller doses throughout the day. Do not take more than the recommended dose. If you have any questions, talk to your health care provider.

Keep magnesium laxatives out of the reach of children.

Talk with your health care provider before taking this medicine if you have a sudden change in your ability to poop (how often you poop or how easy it is to do so) that lasts for two weeks or longer.

Magnesium laxatives usually start working in 30 minutes to six hours. They may cause your poop to be loose, watery, and more frequent. Talk to your health care provider if you have concerns.

Drink 8 ounces of water with each dose of magnesium laxative. Not drinking enough water can be a cause of constipation. Magnesium laxatives may cause diarrhea. Drinking water while taking a magnesium laxative can help you stay hydrated.

Do not take this medicine for longer than one week unless your health care provider tells you otherwise.

Stop taking magnesium and call your health care provider if you have any of the following. These could be symptoms of a serious condition.

  • Rectal bleeding or blood in your stool (poop)
  • No bowel movement after taking this medicine

If you are taking a liquid magnesium laxative, check the label to see if you need to shake it. Some liquid magnesium laxatives need to be shaken well before you measure your dose. Use an accurate measuring device to measure your dose of liquid magnesium laxative. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist what measuring device to use.

If you are taking a granule form of magnesium laxatives (such as Epsom salts), you should dissolve the dose in 8 ounces of water before drinking it. You may add lemon juice to help improve the taste. Follow the instructions on the product label.

Magnesium laxatives may affect how other medicines work. You may need to take magnesium laxatives at a different time than other medicines. Your health care provider can let you know when to take each medicine.

What should I tell my health care provider before using magnesium laxatives?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if magnesium laxatives are right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • Kidney problems
  • Myasthenia gravis or any other nervous system conditions
  • Stomach pain, nausea, or vomiting
  • A change in your pooping habits that lasts for two weeks or longer
  • Already used a laxative for more than seven days
  • Electrolyte problems, such as low or high levels of magnesium, potassium, or sodium
  • Appendicitis
  • Heart problems, including heart block
  • Dehydration
  • Gut problems, including a blockage, tear, or poop stuck in your digestive tract (fecal impaction)

Low-Sodium (Salt) or Low-Magnesium Diet. Tell your health care provider if you are on a low-sodium or low-magnesium diet. Your health care provider will let you know if you should take a magnesium laxative if you have dietary restrictions.

Other Medicines and Supplements. Magnesium laxatives may interact with other medicines and supplements. Before taking magnesium laxatives, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take a magnesium laxative while you are pregnant or trying to get pregnant.

Breastfeeding. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take a magnesium laxative while breastfeeding.

Interactions

Do magnesium laxatives interact with foods or drinks?

There are no known interactions between magnesium laxatives and foods or drinks.

It is unknown if drinking alcohol will affect magnesium laxatives.

Do magnesium laxatives interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking magnesium laxatives.

  • A bisphosphonate, such as alendronate (Binosto, Fosamax), ibandronate, or risedronate (Actonel, Atelvia), which is a medicine commonly used for osteoporosis
  • A tetracycline, such as doxycycline, minocycline, omadacycline (Nuzyra), sarecycline (Seysara), or tetracycline, which is a medicine used to treat infections or other conditions
  • A fluoroquinolone, such as ciprofloxacin (Cipro, Cipro XR, Proquin), levofloxacin, moxifloxacin, or ofloxacin, which is a medicine used to treat certain infections 
  • A diuretic, also called a water pill, which is a medicine used to reduce edema (fluid retention) and blood pressure
  • A product containing zinc, which is a supplement that may be used for low zinc levels

Magnesium laxatives may affect the absorption of many other medicines. Tell your health care provider about all medicines that you take or have recently taken.

This may not be a complete list of medicines that can interact with magnesium laxatives. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much magnesium laxative?

If you or someone else has taken too much magnesium laxative, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of magnesium laxative?

Magnesium laxatives are meant to be taken only when needed. Take them according to the product directions or as your health care provider recommends. Do not take double or extra doses.