Magnesium Supplementation in Mental Health Care

Indications for Serum Magnesium Measurement

Serum magnesium should be measured in patients with gastrointestinal disorders that predispose to magnesium loss (e.g., inflammatory bowel disease, short‑bowel syndrome) because deficiency is common in these conditions. 1
Serum magnesium should be measured in patients receiving medications known to deplete magnesium (e.g., diuretics, proton‑pump inhibitors). 2
Although a serum magnesium < 1.3 mEq/L defines hypomagnesemia, serum levels poorly reflect total body stores since less than 1 % of magnesium resides in blood; intracellular depletion can exist despite normal serum values. [1][3]

Initiate oral magnesium oxide at 12–24 mmol per day (≈400–800 mg elemental magnesium), divided into multiple doses with the largest portion taken at bedtime to take advantage of slower nighttime intestinal transit. Evidence level: expert consensus. [3][4]
If patients develop gastrointestinal intolerance (e.g., diarrhea) with magnesium oxide, switch to organic salts such as magnesium citrate, aspartate, or lactate, which have superior bioavailability despite lower elemental magnesium content. Evidence level: expert consensus. [3][4]

Re‑measure serum magnesium 1–2 weeks after starting therapy when baseline levels were low, aiming for a serum concentration > 0.6 mmol/L (≈1.5 mg/dL). Evidence level: expert consensus. 4
The most frequent adverse effect is dose‑dependent diarrhea; it can be mitigated by reducing the dose or changing to a more tolerable formulation. Evidence level: expert consensus. 4
Avoid magnesium oxide in patients with renal insufficiency because of the risk of hypermagnesemia. Evidence level: guideline‑based recommendation. 5
Do not use magnesium supplementation in patients with severe renal impairment (eGFR < 30 mL/min) without close monitoring of serum magnesium. Evidence level: expert consensus. 3
Signs of hypermagnesemia include muscular weakness, drowsiness, confusion, and, at very high levels, bradycardia and respiratory depression. Evidence level: clinical description. 6

For moderate‑to‑severe depression or anxiety, magnesium should be used as an adjunct to evidence‑based psychotherapy and pharmacotherapy rather than as a standalone treatment. Evidence level: guideline recommendation. 7

Patients most likely to benefit from magnesium supplementation include those with:
- Gastrointestinal disorders associated with malabsorption. 1
- Medication‑induced magnesium depletion. 2
Magnesium is less likely to be effective in patients with severe psychiatric illness that requires intensive psychiatric intervention. Evidence level: guideline recommendation. 7

Do not rely solely on a normal serum magnesium level to rule out deficiency; intracellular depletion may be clinically significant. [1][3]
Do not prescribe high‑dose magnesium in patients with renal impairment without appropriate monitoring for hypermagnesemia. [5][3]