Oral Magnesium Dosing for General Adult Patients
For a general adult patient with no underlying medical conditions, start with the Recommended Daily Allowance of 320 mg/day for women or 420 mg/day for men, and do not exceed the Tolerable Upper Intake Level of 350 mg/day from supplements to avoid adverse effects. 1
Standard Dosing Framework
The National Institutes of Health establishes clear baseline recommendations for magnesium supplementation in healthy adults 1:
- Women: 320 mg elemental magnesium daily 1
- Men: 420 mg elemental magnesium daily 1
- Maximum safe dose from supplements: 350 mg/day (Tolerable Upper Intake Level) 1
These doses represent the Institute of Medicine's Dietary Reference Intake guidelines and should serve as your starting point for any patient without specific medical indications 2.
Form Selection and Bioavailability
Choose organic magnesium salts (aspartate, citrate, lactate, or glycinate) over magnesium oxide or hydroxide for better bioavailability and tolerability. 2 Liquid or dissolvable magnesium products are generally better tolerated than pills 2, 1.
The American Society of Nephrology specifically recommends organic magnesium salts due to superior absorption compared to inorganic forms 2. Magnesium glycinate causes fewer gastrointestinal side effects while maintaining excellent bioavailability 2.
Administration Timing
Administer magnesium at night when intestinal transit is slowest to maximize absorption. 2 This timing recommendation comes from studies in patients with short bowel syndrome but applies broadly to optimize bioavailability 2.
Critical Safety Considerations
Absolute Contraindications
Never prescribe magnesium supplementation if creatinine clearance is <20 mL/min due to life-threatening hypermagnesemia risk. 2, 1 The kidneys are responsible for nearly all magnesium excretion, and impaired renal function prevents adequate elimination 2.
Check renal function before initiating any magnesium supplementation 2, 1. Between creatinine clearance of 20-30 mL/min, use extreme caution and only in emergency situations 2.
Common Side Effects
The most frequent adverse effects include 2:
- Diarrhea
- Abdominal distension
- Gastrointestinal intolerance
These effects are dose-dependent and may require dose reduction 2.
Monitoring Requirements
For patients on stable oral supplementation 2:
- Initial check: 2-3 weeks after starting supplementation
- After dose adjustments: 2-3 weeks following any change
- Maintenance monitoring: Every 3 months once on stable dosing
Target serum magnesium >0.6 mmol/L (>1.8 mg/dL), though recognize that serum levels do not accurately reflect total body magnesium status since less than 1% of total body magnesium is found in blood 2, 1.
Special Populations Requiring Consideration
While you asked about general adults, be aware that certain groups may benefit from supplementation at the RDA level 2:
- Elderly individuals
- Strict vegetarians
- Individuals on calorie-restricted diets
- Pregnant or lactating women
Common Pitfalls to Avoid
Do not assume normal serum magnesium excludes deficiency—less than 1% of total body magnesium is in blood, so normal levels can coexist with significant intracellular depletion 2.
Avoid magnesium oxide for general supplementation purposes unless constipation is specifically desired, as it has poor bioavailability and causes more osmotic diarrhea 2, 1.
Never use magnesium hydroxide or magnesium sulfate (Epsom salts) orally for supplementation—these are potent laxatives with poor absorption 2.
Drug Interactions
Monitor carefully in patients taking 2:
- Digoxin (magnesium deficiency increases sensitivity to digoxin toxicity)
- Diuretics (increase magnesium losses)
- Proton pump inhibitors (reduce magnesium absorption)
- Fluoroquinolones (magnesium may be a risk factor for tendon disorders)