Magnesium
The form matters more than the dose. A clinical guide to matching magnesium to the indication.
Evidence highlight
RBC magnesium deficiency is present in up to 60% of type 2 diabetics and 40% of fibromyalgia patients. Serum magnesium is a poor marker — normal serum can coexist with significant intracellular depletion.
Therapeutic dosing
Magnesium glycinate
200-400mg elemental before bed
Best for sleep, anxiety, muscle relaxation; high bioavailability, low laxative effect
Magnesium threonate
1.5-2g/day (delivering ~144mg elemental)
Crosses blood-brain barrier; for cognitive and neurological indications
Magnesium malate
200-400mg elemental/day
For muscle pain, fibromyalgia, fatigue; malic acid supports ATP production
Magnesium citrate
200-400mg elemental/day
Good general bioavailability; laxative effect at higher doses
Magnesium oxide
Not recommended for systemic use
Very poor absorption (~4%); mainly used for short-term constipation only
Drug interactions
Bisphosphonates (e.g., alendronate) — separate by 2+ hours; magnesium reduces absorption
Antibiotics (quinolones, tetracyclines) — separate by 2+ hours; chelation reduces antibiotic absorption
Levothyroxine — separate by 4 hours; may interfere with absorption
Diuretics (loop, thiazide) — may increase magnesium excretion, worsening deficiency
Proton pump inhibitors — long-term use depletes magnesium; supplementation often needed
Contraindications
Severe renal impairment (eGFR <30) — risk of hypermagnesemia
Heart block
Active bowel obstruction (magnesium citrate/oxide)
Labs to monitor
Mechanism of action
Magnesium is a cofactor in over 300 enzymatic reactions, including ATP synthesis, DNA replication, and glucose metabolism. It modulates NMDA receptors (relevant for pain and sleep), regulates HPA axis response, and is required for vitamin D activation — magnesium deficiency can cause apparent vitamin D resistance even with adequate supplementation.
Clinical note
Never use magnesium oxide for anything other than short-term constipation. The 4% absorption rate makes it clinically useless for systemic deficiency. For patients with insomnia, anxiety, or muscle tension, glycinate is the first choice. Always check RBC magnesium, not serum, for a true picture of status.
Conditions commonly using Magnesium
Commonly combined with
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