Magnesium hydroxide is an inorganic salt used to treat occasional constipation in children and adults. It belongs to a class of medications known as saline laxatives and is available under multiple brand names and in several forms.
Magnesium hydroxide works by drawing water into the intestinal tract. The water triggers bowel movements and softens stools so they are easier to pass. This compound can also be used to relieve heartburn and indigestion and is a common component of antacids like milk of magnesia.
In this post, we’ll talk about the benefits of taking magnesium hydroxide, discuss some of its common side effects, and explore how taking magnesium citrate might be a better option for treating constipation or other digestive issues.
How to Take Magnesium Hydroxide
Magnesium hydroxide is available as a tablet that you swallow, a chewable tablet, or as a liquid in suspension. When it is mixed with water, magnesium hydroxide is called milk of magnesia.
It is usually taken once a day, typically at bedtime, but you can divide the dose throughout the day. Follow your doctor or pharmacist’s directions (or the labelling on the package) carefully and take as directed.
Do not give children magnesium hydroxide products that are made for adults. Medication dosages and strengths for children will be different, so consult your doctor for advice.
Whether you’re taking magnesium hydroxide as a chewable tablet, tablet, or in liquid form, make sure to drink a full 8-ounce glass of water with your dose.
Magnesium hydroxide is intended to be taken only on a short-term basis. Do not take this medication for longer than 7 days without talking to a health care provider.
Potential Side Effects of Magnesium Hydroxide
Common side effects of magnesium hydroxide include:
- Watery, loose, or more frequent bowel movements
- A decreased sense of taste
Stop using magnesium hydroxide and call 911 or your doctor immediately if you have:
- Rectal bleeding
- Severe diarrhea, nausea, or vomiting
- No bowel movement more than 6 hours after taking the medication
- Worsening symptoms
- Signs of an allergic reaction to this medication, like hives, trouble breathing, or swelling of your face, throat, or tongue
Our disclaimer: Our goal is to provide you with the most current information possible, but medications affect each person differently. We cannot guarantee that this information includes all possible side effects of magnesium hydroxide, and this information is not a substitute for medical advice. Before you start taking any medications, discuss any possible side effects or interactions with your healthcare provider who knows your medical history.
Possible Interactions with Magnesium Hydroxide
The following medications and supplements can interact with magnesium hydroxide:
- Seizure medicines such as ethotoin and phenytoin
- Vitamin D
- Medicines for osteoporosis like etidronate, alendronate, risedronate and tiludronate
- Medicines for fungal infections like itraconazole and ketoconazole
- Phenothiazines like mesoridazine, chlorpromazine, prochlorperazine, and thioridazine
- Sodium polystyrene sulfonate
- Other magnesium-containing laxatives, antacids, or supplements
Not all interactions are serious, but some medications and supplements may affect the potency of drugs and supplements. We recommend that you give your healthcare provider a list of everything you’re currently taking, so they can assess the potential for interactions.
How Magnesium Hydroxide Can Affect Magnesium Levels in Your Body
Researchers have found that excessive consumption of magnesium hydroxide can (paradoxically) lead to magnesium deficiency (hypermagnesemia). This paradoxical or unexpected effect is only observed when individuals truly take an excessive amount of magnesium hydroxide.
A 2008 study in the Journal of Emergency Medicine stated:
“…a case of paradoxical hypomagnesemia developed after excessive ingestion of magnesium hydroxide. A 39-year-old woman was presented to the emergency department complaining of severe watery diarrhea and carpopedal spasm after ingesting a handful of magnesium hydroxide tablets. The laboratory tests detected hypomagnesemia, hypocalcemia, and normokalemia. Calcium gluconate was given to the patient, but her symptoms did not improve shortly. The symptom disappeared spontaneously 2 days after the watery diarrhea subsided. This case shows that an overdose of magnesium hydroxide, which leads to massive diarrhea, might induce hypomagnesemia unexpectedly. This case also suggests that it should be treated, as well as typical magnesium deficiency.”
If you are taking magnesium hydroxide and experience symptoms of low magnesium levels—such as nausea, vomiting, muscle spasms, loss of appetite, or personality changes — contact your doctor immediately.
Do You Need Magnesium Hydroxide for Constipation?
Magnesium hydroxide is typically used for constipation, as discussed. There are several lifestyle changes you can also make to help keep you regular. Here are a few constipation prevention ideas to consider:
- Get regular exercise, even a few minutes of walking a day.
- Drink plenty of water
- Limit the amount of processed food you eat
- Increase your intake of fiber-rich foods like fruits, vegetables, and whole grains
- Go to the bathroom as soon as you feel the urge (waiting can cause constipation)
It’s also worth noting that magnesium hydroxide is not the only magnesium supplement for constipation. In fact, all forms of magnesium help to relax the bowels.
Magnesium citrate may be the most popular form of magnesium for constipation and has multiple health benefits, as we’ll discuss.
Alternatives to Magnesium Hydroxide for Occasional Constipation
If you suffer from constipation, acid reflux, or an upset stomach, you may find that supplementing your diet with magnesium citrate is a better option.
Like magnesium hydroxide, magnesium citrate achieves an osmotic laxative effect by drawing water into the intestine (making stools easier to pass) and relaxing the muscle in the intestine so it is easier to have a bowel movement.
Magnesium citrate, however, includes citric acid, which helps to make the magnesium more absorbable even for those who have low stomach acid. Insufficient hydrochloric acid or low stomach acid is a common issue, especially as we age.
Magnesium hydroxide, on the other hand, can only be absorbed if you have enough hydrochloric acid. What’s more, the alkaline properties of magnesium hydroxide could interfere with proper digestion, exacerbating symptoms of heartburn, acid reflux, or GERD.
Research shows that magnesium citrate is very well absorbed, so the magnesium molecule readily passes through the wall of the intestine into the bloodstream, where calming magnesium can be carried to cells throughout the body.
Award-winning Natural Calm® magnesium citrate powder is an easily-absorbable magnesium citrate supplement that dissolves in liquid, creating a delightful fizzy beverage you can drink hot or cold.
If you are experiencing constipation or acid reflux, talk to your healthcare provider to see if Natural Calm® might give you relief from your symptoms.
- “Magnesium Hydroxide: MedlinePlus Drug Information.” Medlineplus.gov, 2019, medlineplus.gov/druginfo/meds/a601073.html. Accessed 22 Sept. 2023.
- Elsevier, Inc. “Magnesium Hydroxide Suspension: Uses & Side Effects.” Cleveland Clinic, 2023, my.clevelandclinic.org/health/drugs/19211-magnesium-hydroxide-suspension. Accessed 22 Sept. 2023.
- Joo Suk Oh. “Paradoxical Hypomagnesemia Caused by Excessive Ingestion of Magnesium Hydroxide.” American Journal of Emergency Medicine, Elsevier BV, Sept. 2008, https://doi.org/10.1016/j.ajem.2008.01.030. Accessed 22 Sept. 2023.
- “Magnesium Hydroxide: Uses, Interactions, Mechanism of Action | DrugBank Online.” Drugbank.com, DrugBank, 2018, go.drugbank.com/drugs/DB09104. Accessed 22 Sept. 2023.