Introduction
Magnesium is an essential mineral that plays a role in over 300 enzyme reactions in the human body. Getting enough magnesium is important for blood sugar control, nerve functioning, blood pressure regulation, energy production and more. While magnesium is generally well tolerated, there are some potential side effects to be aware of when taking magnesium supplements.
Common side effects
For most people, supplementing with magnesium is unlikely to cause severe side effects. However, taking too much magnesium or taking it in forms that the body absorbs rapidly can sometimes lead to:
- Diarrhea
- Nausea
- Abdominal cramping
- Bloating
These mild gastrointestinal side effects often resolve quickly when intake is reduced. They occur because magnesium has an osmotic effect, meaning it pulls water into the intestines which can stimulate the bowel to move more frequently.
Dosage considerations
To avoid loose stools, gas and urgent bowel movements, it’s recommended to start with a lower dose of magnesium and increase slowly over time. Taking magnesium with food can also help minimize side effects.
The tolerable upper intake level (UL) for magnesium established by the Institute of Medicine is 350 mg per day for adults. This is the maximum amount considered safe for the majority of healthy individuals.
Exceeding the UL regularly can increase the risk of diarrhea and abdominal discomfort. However, under medical supervision, higher doses may be used to treat a deficiency.
Forms that cause diarrhea
Some forms of magnesium supplements tend to cause looser stools and diarrhea more easily because of differences in bioavailability:
- Magnesium citrate
- Magnesium oxide
- Magnesium chloride
- Magnesium glycinate
These types dissolve completely in water and are readily absorbed. Start with a lower dose if taking these forms and increase gradually.
Slow-release forms
Forms of magnesium that dissolve slower in the intestines may be less likely to cause diarrhea. These include:
- Magnesium orotate
- Magnesium carbonate
- Magnesium sulfate
- Magnesium gluconate
Slow-release tablets and capsules can also minimize side effects. Look for descriptions like “timed-release” or “extended-release” on the label.
Who is more sensitive?
Some individuals may experience loose stools from magnesium more easily including:
- People with digestive conditions like IBS, Crohn’s disease or ulcerative colitis
- Those who have had a section of bowel removed
- People taking medications that slow bowel transit time like opioids
- Older adults tend to absorb magnesium better so require lower doses
If you have a health condition that affects digestion or take medications that cause constipation, speak to your healthcare provider before starting magnesium.
Interactions with medications
Magnesium can interact with certain medications. Taking magnesium along with these drugs can increase the risk of adverse effects:
- Digoxin (Lanoxin) – used for heart failure and arrhythmias
- Bisphosphonates like alendronate (Fosamax) – used to treat osteoporosis
- Antibiotics including quinolones, tetracyclines and aminoglycosides
- Diuretics (“water pills”)
Magnesium may decrease absorption of these medications when taken at the same time. Check with your doctor about potential interactions and proper timing of doses.
Too much magnesium
Consuming extremely high amounts of magnesium through diet alone is unlikely. However, taking high doses of supplements long-term can potentially lead to more severe side effects including:
- Abnormally low blood pressure
- Changes in heart rhythm
- Confusion
- Muscle weakness
- Difficulty breathing
- Kidney dysfunction
Symptoms of magnesium toxicity generally begin at blood levels higher than 4-5 mg/dL. Toxicity is rare in people with normal kidney function taking less than the UL.
Some populations at higher risk include:
- People with impaired kidney function
- Infants under 6 months old
- Individuals taking magnesium intravenously
Talk to your doctor about magnesium safety if you have kidney problems or other health conditions.
Medications with magnesium
Some laxatives, antacids and products used to treat heartburn contain magnesium compounds like magnesium hydroxide or magnesium oxide.
Using these alongside magnesium supplements can easily exceed the UL and irritate the digestive tract. Read labels carefully and track total intake from all sources.
Signs of deficiency
While too much magnesium causes loose stools, a deficiency can lead to the opposite problem—constipation.
Other potential signs of magnesium deficiency include:
- Muscle twitches, tremors or spasms
- Restless leg syndrome
- Impaired athletic performance
- Weakness and fatigue
- Leg cramps or Charlie horses
- Migraines and headaches
- High blood pressure
- Type 2 diabetes
- Osteoporosis
- Depression and anxiety
If you are experiencing any of these symptoms, check with your doctor. They may recommend having your magnesium levels tested.
Food sources of magnesium
Rather than supplements, getting magnesium from whole food sources can help minimize adverse effects. Foods high in magnesium include:
- Dark leafy greens like spinach and kale
- Nuts and seeds
- Fatty fish such as mackerel and salmon
- Avocados
- Bananas
- Legumes, beans and lentils
- Whole grains
- Low-fat dairy
Aim to include a variety of magnesium-rich foods in your diet daily.
Who may need a supplement?
While most people can get adequate magnesium through diet alone, supplements may be beneficial for:
- Those with a diagnosed magnesium deficiency
- People with digestive disorders like celiac disease or IBS
- Older adults
- Individuals with type 2 diabetes
- People taking medications like diuretics, PPIs or chemotherapy
- Athletes who need extra for performance and recovery
If you fall into one of these groups, speak with your doctor about whether magnesium supplementation may be helpful.
Forms for specific uses
Different forms of magnesium have been studied for various therapeutic applications:
- Magnesium glycinate – taken for anxiety, depression, trouble sleeping
- Magnesium oxide – used as a laxative for constipation
- Magnesium chloride – used topically for muscle cramps and soreness
- Magnesium citrate – taken for migraine headache prevention
- Magnesium threonate – taken to improve age-related memory decline
The evidence for these uses is still emerging. Work with a healthcare professional to determine which form and dosage may be appropriate based on your individual needs and health status.
Safety tips
To use magnesium supplements safely:
- Start with a lower dose and work up gradually as tolerated
- Spread doses throughout the day instead of a single large dose
- Take with food to enhance absorption and minimize side effects
- Increase fluid intake unless instructed otherwise by your doctor
- Avoid giving magnesium supplements to children unless recommended by a pediatrician
Discontinue use and contact your healthcare provider if you experience severe diarrhea, significantly low blood pressure, irregular heartbeat or other concerning symptoms.
The bottom line
When taken appropriately, magnesium is generally well tolerated with few side effects. Mild gastrointestinal upset is possible, especially when taking forms that are more bioavailable. To reduce the chance of loose stools or diarrhea, start with a lower dose, increase slowly and take magnesium with meals.
While there is no established upper limit for obtaining magnesium through food, the UL for supplements is 350 mg per day for adults. Consuming extremely high amounts can potentially lead to magnesium toxicity. Talk to your doctor about the appropriate dosage for your needs and health status.
| Form | Common Uses | Considerations |
|---|---|---|
| Magnesium glycinate | Anxiety, sleep, muscle relaxation | More absorbable form, moderate risk of loose stools |
| Magnesium oxide | Constipation relief | Poorly absorbed, high laxative effect |
| Magnesium citrate | Migraine prevention, constipation | Readily absorbed, likely to cause diarrhea |
| Magnesium threonate | Brain health and cognition | Expensive, may improve memory |
Conclusion
Magnesium supplements are generally well tolerated when used appropriately and can provide benefits for those with inadequate intakes. However, exceeding the recommended upper limit, especially from supplements, does come with the risk of gastrointestinal side effects like diarrhea. Starting with a lower dose, increasing slowly, taking with food and using slow-release forms can help minimize the chance of adverse effects.
