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Magnesium supplement Pregnancy: eMC 4.6: Effectiveness and safety in pregnancy not established - use in pregnancy only if the benefits outweigh the potential risks; long-term data from treatment of pre-eclampsia do not indicate malformative or feto/neonatal toxicity of magnesium. Avoid aminoglycoside antibiotics during this period. Can be used during breast-feeding - magnesium glycerophosphate/metabolites are excreted in human milk but no effects on the breastfed infant are anticipated at therapeutic doses. No effects on male or female fertility anticipated.

Magnesium glycerophosphate

Brand names: Neomag

Magnesium glycerophosphate is an oral magnesium salt used for the treatment and prevention of chronic magnesium deficiency, often favoured for its tolerability.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 4-8 mmol (1-2 tablets) three times a day, giving a total of 12-24 mmol per day in divided doses
Route: Oral (tablet may be broken into quarters and chewed or swallowed with water)
Frequency: Three times a day
eMC SPC 4.2 (Neomag): adults over 18 years - 'Starting doses for adult patients are recommended as 4-8 mmol (1-2 tablets) administered 3 times a day. This equates to a total dose of 12 to 24 mmol per day taken in divided doses.' The dosage regimen should be adjusted according to the individual patient's serum total magnesium level. Patients with severe, symptomatic hypomagnesaemia should receive intravenous magnesium repletion for acute recovery of magnesium levels before receiving oral magnesium glycerophosphate. Serum magnesium should be monitored at regular intervals (e.g. every 3-6 months), particularly in children and in renal impairment. Elderly: no dose adjustment necessary. Paediatric doses in the SPC are not weight-based: below 4 years not recommended (insufficient information); 4 to 12 years - 4 mmol (1 tablet) twice a day (total 8 mmol/day); 12 to 18 years - 4 mmol (1 tablet) three times a day (total 12 mmol/day); paediatric use only under the supervision of physicians experienced in the management of children with hypomagnesaemia and if benefits outweigh risks - verify against a children's formulary. Co-administration of potassium and calcium supplements may be necessary since associated loss of these cations is common in severe magnesium deficiency. Absorption may be reduced after extensive bowel resection (main absorption sites are jejunum and ileum).

Dose adjustments

Renal

eMC 4.2/4.3: Contraindicated in severe renal impairment (GFR < 30 ml/min). No dose adjustment necessary in mild to moderate renal impairment. Monitor serum magnesium at regular intervals in renal impairment - hypermagnesaemia is possible with impaired renal function.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Hypersensitivity to the active substance or to any of the excipients
  • Severe renal impairment (glomerular filtration rate < 30 ml/min)
  • Phenylketonuria (the tablets contain aspartame)
  • Hyperphosphataemia (the tablets contain phosphate)

Side effects

  • Diarrhoea - usually dose dependent; if it occurs reduce the daily dose and increase again gradually later if needed
  • Hypermagnesaemia - possible with higher doses and with impaired renal function

Interactions

  • Digoxin and loop diuretics are magnesiuretic and may affect magnesium balance; magnesium deficiency may enhance digoxin toxicity
  • Cellulose sodium phosphate and edetate disodium bind magnesium - do not take magnesium supplements within 1 hour of these drugs
  • Fluorides and tetracycline - separate doses by 2 to 3 hours or more
  • Aminoquinolines, quinidine and derivatives, nitrofurantoin, penicillamine, iron, bisphosphonates (e.g. alendronate, risedronate), eltrombopag, nitroxoline - take magnesium 3 to 4 hours before or after these drugs to avoid impaired absorption
  • Increased magnesium losses (magnesium dose adjustment may be needed) with aminoglycosides, cisplatin, ciclosporin A, diuretics (thiazides, furosemide), EGF-receptor antagonists (cetuximab, erlotinib), proton pump inhibitors (omeprazole, pantoprazole), foscarnet, pentamidine, rapamycin and amphotericin B
  • General rule: a 2 to 3 hour interval should be respected between magnesium and other medicinal products where possible

Clinical monograph

How it works

It provides elemental magnesium, an essential cofactor in many enzymatic, neuromuscular and cardiac processes, to correct hypomagnesaemia.

Prescribing in practice

  • Use cautiously with reduced exposure in renal impairment owing to the risk of magnesium accumulation and hypermagnesaemia.
  • Although often better tolerated than other salts, it can still cause diarrhoea, which may limit the dose.
  • It may impair absorption of certain medicines, including some antibiotics, so administration should be spaced apart.

Monitoring

Monitor serum magnesium, and renal function where appropriate, to guide ongoing replacement.

Counselling the patient

  • Take with food to improve tolerance.
  • Report persistent loose stools.
  • Keep an interval between this and certain other medicines as advised.

Evidence & guidelines

Magnesium glycerophosphate is an established oral option for correcting chronic magnesium deficiency in UK practice.

Reference: Confirm identity and dosing against the manufacturer SPC (eMC) and NICE. Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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