Magnesium

What is therapeutic magnesium?

Magnesium, a naturally occurring mineral, is essential for the functioning of many different systems in the body, including the nerves and muscles. It is available over the counter (OTC) formulated as a supplement for people who don’t get enough magnesium from dietary sources. It can also be used for targeted therapy, either OTC, by prescription, or administered by injection or intravenous infusion in a healthcare setting.

This guide provides key information about therapeutic magnesium used to treat a specific medical condition, including dosing formulations, side effects, warnings, and tips.

What is magnesium used to treat?

There are several different formulations of therapeutic magnesium with various indications.

Magnesium citrate

Magnesium citrate is often used as a short-term treatment for acute but significant constipation. It’s a saline laxative that softens the stools by helping them to hold more water, which allows them to move more easily through the digestive tract. This form of magnesium is also used to empty the intestinal tract before an endoscopic procedure or surgery.¹

Magnesium hydroxide

The effects of magnesium hydroxide on the body depend on the dose taken. Low doses work more like an antacid in the stomach. Similar to magnesium citrate, higher doses of magnesium hydroxide act as a saline laxative in the colon to treat occasional constipation. It also stimulates the release of messenger chemicals that work to bring water from the cells into the intestines, which helps stools move through the colon.² ³

Magnesium oxide

Magnesium oxide is used as a one-time saline laxative for emptying the bowel before surgery and testing. Like magnesium hydroxide, this form also treats gastrointestinal (GI) troubles, including heartburn, indigestion, and constipation. People with magnesium deficiency can use magnesium oxide as a supplement to boost their levels.⁴

Magnesium sulfate

OTC oral forms of magnesium sulfate are used for short-term constipation relief.⁵

Magnesium sulfate may be used to improve magnesium levels in people who are deficient in the mineral.

It is administered by injection in a healthcare setting to prevent seizures in preeclampsia and control them in eclampsia, both serious complications of pregnancy. And it’s also used intravenously as a first-line treatment for torsades de pointes, an uncommon type of heart rhythm disorder.⁶ ⁷

Dosage forms and strengths

Therapeutic magnesium is available in a broad range of forms and strengths, including the following:

• Magnesium citrate:⁸

  • Tablet: 100mg

  • Liquid: 290mg/5mL

• Magnesium hydroxide (Dulcolax, Phillips’ Milk of Magnesia, Pedia-Lax):⁹

  • Chewable tablet: 311mg, 400mg, 1200mg

  • Liquid suspension: 400mg/5mL, 800mg/5mL, 1200mg/15mL, 2400mg/10mL, 7.75%

• Magnesium oxide:¹⁰

  • Tablet: 400mg

  • Capsule: 140mg

• Magnesium sulfate:¹¹ ¹² ¹³

  • Oral forms, including tablets, capsules, granules, and powder (to mix with water) in various strengths¹⁴ ¹⁵

  • Injectable solution: 40mg/mL, 80mg/mL, 50%, 80%

  • Infusion solution: 1g/100mL, 2g/100mL

This outline of available doses covers many of the most common strengths, but others are available for different indications.

How do you take magnesium?

How you take magnesium depends on the form you take and the condition you’re treating. How often you take it also depends on your strength.

You can take the oral forms with or without food, but taking magnesium with a meal can reduce stomach upset. Take each dose with a full glass of water.¹⁶

Unlike the other three types, magnesium sulfate is also available in a non-oral form administered by a qualified professional in a healthcare setting. It’s delivered intravenously or intramuscularly. Occasionally, it’s administered intraosseously (into the bone marrow) when other routes are not feasible.¹⁷ ¹⁸

You should always follow the product label or your doctor's instructions when taking magnesium.

Seeing results

How long magnesium takes to work largely depends on the type, formulation, and dose you're taking. As expected, its effects also vary somewhat based on the condition being treated and its severity. People taking an oral form of magnesium citrate for its laxative effects, for example, can expect to see results within 30 minutes to six hours.¹⁹ ²⁰

In its non-oral form, magnesium sulfate produces anticonvulsant effects immediately when administered intravenously and within an hour when delivered intramuscularly.²¹

Who should not take magnesium?

Magnesium is not appropriate for people who have had a previous allergic reaction to the mineral. 

Additionally, you should exercise caution and may need a dose adjustment if you have any of the following conditions that can affect your body’s handling of the mineral:²² ²³

• Colostomy or ileostomy

• Diverticulitis

• Ulcerative colitis

• Appendicitis

• Fecal impaction

• Rectal fissures

• Intestinal obstruction or perforation

• Kidney impairment

• Botulism

• Electrolyte imbalance

• Dehydration

• Undiagnosed abdominal pain²⁴ 

• Myasthenia gravis or other neuromuscular disorders²⁵

Intravenous administration of magnesium is contraindicated for patients with heart block, heart damage, or diabetic coma. It is also not suitable for people with excess magnesium or calcium in the blood, so be sure to discuss all your medical conditions with your doctor.²⁶ ²⁷

Potential side effects of magnesium

Magnesium can trigger side effects. Except in cases of extremely high intakes, the unwanted effects are typically limited to:²⁸

• Abdominal cramping

• Diarrhea

• Nausea

However, some people taking magnesium experience less common or severe adverse effects, including the following:²⁹ ³⁰ ³¹

• Low blood pressure 

• Muscle weakness 

• Respiratory depression

• Irregular heartbeat

• Cardiac arrest or reduced cardiac function

The intravenous form carries its own potential risks, but your healthcare team will monitor for adverse reactions. Possible side effects exclusive to intravenous magnesium sulfate include:³²

• Circulatory collapse 

• Fluid buildup in the lungs 

• Slowed reflexes 

• Flushing 

• Excessive or abnormal sweating 

• Low calcium or phosphorus or high potassium in the blood 

• Visual changes 

If you experience side effects while taking magnesium, speak with your doctor. If your symptoms are severe, seek urgent medical care.

Overdose

Magnesium overdose can result from taking too much, but it may also develop from taking the mineral as prescribed or according to the label in people whose bodies excrete magnesium inefficiently or absorb it too efficiently. You may face a higher risk if you are:³³

• On dialysis for kidney impairment

• Undergoing cancer treatment

• Receiving high doses of magnesium to prevent seizures in preeclampsia

Early symptoms of magnesium toxicity may include any of the following:

• Diarrhea

• Nausea, vomiting

• Low blood pressure

• Muscle weakness

• Visual changes

• Flushing

• Extreme fatigue

Left untreated, rising magnesium levels may lead to:

• Loss of reflexes, muscle paralysis

• Respiratory depression

• Low blood pressure

• Heart block, rhythm abnormalities, slowed heart rate

• Cardiac arrest

If you suspect you may be experiencing symptoms of a magnesium overdose, stop taking it and seek medical attention immediately. Depending on the severity of your symptoms, either speak with your doctor or call 911.

Allergy information

Monitor for symptoms of a drug allergy while taking magnesium, even if you’ve taken it before. Symptoms of an allergic reaction may include any of the following:

• Wheezing, difficulty breathing

• Rash, hives, itching

• Swelling of the face, lips, tongue, or mouth

• Lightheadedness, fainting

• Vomiting

• Rapid heart rate

• Loss of consciousness

If you experience allergic symptoms while taking magnesium, stop taking it and speak with your doctor. If your symptoms are severe, call 911 or go to your nearest emergency department.

Long-term use of magnesium

For the treatment of constipation, heartburn, indigestion, torsades de pointes, and the prevention of seizures in preeclampsia, magnesium is intended for short-term and one-time or occasional use. Using laxatives like magnesium long-term for constipation, in particular, can lead to severe adverse effects, including dehydration and electrolyte imbalances.³⁴ ³⁵

In contrast, people taking magnesium to treat a deficiency often take it long-term, and doing so can potentially have beneficial effects, including:

• Improved arterial stiffness³⁶

• Decreased blood pressure³⁷

• Enhanced glucocorticoid metabolism³⁸ 

• Reducing symptoms in polycystic ovarian syndrome (PCOS)³⁹

• Improved bone mineral density⁴⁰

Magnesium and pregnancy

The US Food and Drug Administration (FDA) has assigned the oral forms of magnesium to pregnancy category A. Category A drugs are considered safe during pregnancy as studies in pregnant women have not demonstrated any risks to the fetus.⁴¹

Magnesium sulfate given by injection has been assigned to pregnancy category D. Risks to the fetus are seen only in the off-label, unapproved uses of this formulation.⁴² ⁴³

Magnesium and breastfeeding

All forms of magnesium are considered safe to take while breastfeeding. However, it’s a good idea to discuss your plans with your healthcare professional before taking any medications, vitamins, herbs, or supplements while nursing.⁴⁴ ⁴⁵

Missed doses

If your doctor has recommended that you take magnesium on a fixed schedule and you forget it, take the missed dose as soon as you remember.

If it's almost time for the next dose, skip the missed dose and continue with your regular dosing schedule. Don't take a double amount to make up for the missed dose, as taking too much may lead to magnesium toxicity.

Drug interactions

Magnesium may interact with other medications you're currently taking, making them less effective. Here are some of the drugs known to interact with magnesium:⁴⁶

• Alendronate (Binosto)

• Antibiotics, such as levofloxacin, ciprofloxacin (Cipro), clindamycin (Cleocin), doxycycline (Vibramycin), amikacin, cefdinir, and others

• Antidepressants like clomipramine (Anafranil), mirtazapine (Remeron), milnacipran (Savella), paroxetine (Paxil), venlafaxine (Effexor XR), and vortioxetine (Trintellix)

• Antihistamines like fexofenadine (Allegra)

• Antipsychotic drugs, including chlorpromazine and perphenazine 

• Antivirals like baloxavir marboxil (Xofluza), raltegravir (Isentress), cabotegravir (Apretude), bictegravir (Biktarvy), acyclovir (Zovirax), and others

• Asthma medicines like albuterol, salmeterol (Serevent Diskus)

• Cancer drugs, such as irinotecan (Camptosar), carboplatin, capecitabine (Xeloda), decitabine (Dacogen), and methotrexate

• Diabetes medications like sitagliptin (Januvia) and liraglutide (Saxenda) 

• Digoxin (Lanoxin)

• Diuretics, including:

  • Angiotensin-converting enzyme (ACE) inhibitors like captopril and benazepril (Lotensin)

  • Thiazides like chlorothiazide (Diuril) and hydrochlorothiazide

• Donepezil (Aricept)

• Dronabinol (Marinol)

• High blood pressure medications, including aliskiren (Tekturna), amiloride, metolazone, valsartan, spironolactone (Aldactone)

• Immune modulators, such as cyclosporine (Gengraf), rituximab (Rituxan), tacrolimus (Prograf)

• Levothyroxine (Levoxyl, Unithroid)

• Non-steroidal anti-inflammatories (NSAIDs), such as aspirin, celecoxib (Celebrex), diflunisal, ketorolac, and meloxicam (Mobic)

• Pain medications like tramadol, gabapentin (Neurontin), oxycodone, oliceridine (Olinvyk), and morphine

• Sedatives like midazolam (Versed) and diazepam (Valium)

• Seizure medicines, including cannabidiol (Epidiolex), zonisamide (Zonegran), topiramate (Topamax), lamotrigine (Lamictal), and others

• Steroids, such as corticotropin, cortisone, dexamethasone, prednisolone, and others

• Cocaine

Can I drink alcohol while taking magnesium?

There are no known interactions between alcohol intake and magnesium.

What to discuss with your doctor before starting magnesium

Before you start magnesium, it's vital that your doctor knows everything about you. This is important because magnesium can be purchased without a prescription, so many people start taking it without considering the possible negative effects. Before taking magnesium, discuss the following with your doctor:⁴⁷ 

• Any allergies to magnesium or any other medications or ingredients in the drug 

• All prescription and nonprescription medications, nutritional supplements, vitamins, and herbal products you take regularly or occasionally

• All medical conditions you have (or have ever had), particularly stomach problems, kidney disease, or intestinal disease (such as ulcerative colitis, diverticulitis, or a colostomy)

• If you’re pregnant, planning a pregnancy, or breastfeeding

• Symptoms of nausea, vomiting, or a sudden change of bowel habits lasting more than 14 days

• If you’re on a low-salt, low-magnesium, or other special diet

Stopping magnesium

The safety of stopping magnesium depends on the condition you’re treating. 

For most indications, people take magnesium short-term or occasionally. If you take it for one of the following conditions, there’s no reason to continue treatment once the situation has been resolved: 

• Constipation

• Heartburn

• Indigestion

• Bowel prep

• Torsades de pointes

• Seizure prevention in preeclampsia

However, if you take magnesium because you’re deficient in the mineral, stopping it will likely trigger a return of your condition unless you’ve made significant changes to include more magnesium-rich foods in your diet. Magnesium deficiency can have severe consequences, so if you’re taking it for this reason, you should seek guidance from your doctor before stopping. 

Drug approval history

• 1941: The US FDA approved magnesium sulfate.⁴⁸

While the other forms are approved ingredients according to the US FDA’s OTC Active Ingredients list, information about their approval dates is not available.⁴⁹

Tips for taking magnesium

As with any medication, you should take magnesium as your doctor or pharmacist recommends to increase its effectiveness and prevent adverse effects and potential drug interactions. Here are some tips to help you take magnesium safely:⁵⁰ ⁵¹

• Drink plenty of water to reduce the risk of dehydration while taking magnesium. 

• Stop taking magnesium and consult your healthcare professional if you experience rectal bleeding or fail to have a bowel movement after taking it for constipation.  

• Keep your medications in the container they came in and tightly closed. 

• Store magnesium at room temperature, away from excess heat and temperature. 

• Keep all medications and supplements away from children.

Frequently asked questions

Does taking magnesium make you tired the next day?

Drowsiness is not a commonly reported side effect of magnesium. However, it’s impossible to predict how your body will react to a new medication. If you notice anything unusual while taking magnesium, speak with your doctor.

Is taking supplemental magnesium safe?

Magnesium is safe for most people, but it’s not suitable for everyone. While it’s available without a prescription, it’s best to speak with your doctor before taking this or any other medication.