Is magnesium glycinate (Mg) effective for treating constipation?

Magnesium for Constipation: Effectiveness and Considerations

Magnesium oxide is effective for treating constipation, with significant improvement in bowel movements and stool consistency, but magnesium glycinate specifically has not been studied for constipation treatment. 1, 2

Effectiveness of Magnesium for Constipation

• Magnesium oxide (MgO) has demonstrated effectiveness for chronic idiopathic constipation (CIC) with a conditional recommendation from clinical guidelines, though based on very low certainty evidence 1
• Studies show that 68% of patients respond to magnesium oxide compared to 19% with placebo (RR 3.32), with significant improvements in:
  • Stool frequency (3.72 more bowel movements per week) 2, 3
  • Stool consistency (1.14 point improvement on Bristol Stool Scale) 2, 3
• Magnesium oxide significantly improves quality of life measures in patients with constipation 3, 4

Mechanism of Action

• Magnesium acts primarily through an osmotic effect in the intestinal lumen, where poorly absorbable magnesium ions cause water retention, increasing fluidity of intestinal contents 5
• This osmotic action results in softer stools and increased bowel movements 5

Important Considerations and Limitations

• Magnesium glycinate specifically has not been evaluated in randomized controlled trials for constipation 2
• Only magnesium oxide has been thoroughly evaluated in clinical trials; the bioavailability and efficacy of other formulations (including glycinate) are unknown 1
• Magnesium oxide should be avoided in patients with renal insufficiency due to risk of hypermagnesemia 1
• Approximately 15% of orally administered magnesium oxide is absorbed systemically, with the remainder excreted in feces 6
• Guidelines suggest starting at a lower dose of magnesium oxide, which can be increased if necessary 1

Alternative First-Line Options for Constipation

• Polyethylene glycol (PEG) is strongly recommended as first-line therapy for chronic constipation based on moderate certainty evidence 1
• Fiber supplements, particularly psyllium, are recommended as first-line therapy, especially for those with low dietary fiber intake 1
• For opioid-induced constipation, stimulant laxatives are often preferred, with methylnaltrexone as an option for refractory cases 1, 7

Practical Recommendations

• For chronic constipation, start with non-pharmacological approaches (increased fluid intake, physical activity, proper toileting position) 1, 7
• If medication is needed, polyethylene glycol or psyllium should be considered before magnesium products 1
• If using magnesium oxide, start at a lower dose and increase as needed, with typical dosing in studies being 1.5g/day, though lower doses of 500mg-1g/day are often used clinically 1
• Monitor renal function in patients taking magnesium supplements, especially those with known renal impairment 1