Magnesium Dosage Guide: How Much to Take by Age, Goal, and Form
Most people get 200 to 300 mg of magnesium from food, leaving a gap of 100 to 200 mg from supplements for most adults. The right dose depends on your age, goal, and form. Doses throughout this guide refer to elemental magnesium: the actual mineral content, not the total capsule weight.
Quick answer
- -Most adults need 200 mg of elemental magnesium per day from supplements, on top of dietary intake.
- -Upper limit from supplements is 350 mg per day of elemental magnesium.
- -Glycinate for sleep, anxiety, and stress; citrate for constipation and cheap repletion.
- -Start low (100 to 200 mg), take with food, and increase gradually.
Elemental Magnesium: The Only Number That Matters
Magnesium supplements always list two numbers: the total compound weight and the elemental magnesium content. Only the elemental number counts. Manufacturers sometimes highlight the larger compound weight on the label because it looks more impressive, so read carefully.
| Label says | Elemental magnesium | What it means |
|---|---|---|
| 500 mg magnesium glycinate | ~100 mg | Glycine accounts for ~80% of the weight |
| 500 mg magnesium citrate | ~80 mg | Citric acid accounts for ~84% of the weight |
| 400 mg magnesium oxide | ~240 mg (only 4 to 5% absorbed) | High elemental, poor absorption |
| 200 mg magnesium threonate | ~20 mg | Very low per-capsule content |
A reputable label lists both numbers clearly, usually in the Supplement Facts panel. If a product lists only the compound weight without the elemental content, treat it as a warning sign and look for a better brand.
Recommended Daily Allowance by Age and Life Stage
These are the US Institute of Medicine's Dietary Reference Intakes for total magnesium per day, combining food and supplements. Most adults get 200 to 300 mg from food, so the supplement dose needed to reach the RDA is usually 100 to 200 mg.
| Group | RDA total daily |
|---|---|
| Children, 4 to 8 years | 130 mg |
| Children, 9 to 13 years | 240 mg |
| Teen boys, 14 to 18 | 410 mg |
| Teen girls, 14 to 18 | 360 mg |
| Adult men, 19 to 30 | 400 mg |
| Adult men, 31+ | 420 mg |
| Adult women, 19 to 30 | 310 mg |
| Adult women, 31+ | 320 mg |
| Pregnant women | 350 to 360 mg |
| Breastfeeding women | 310 to 320 mg |
Therapeutic Dose by Goal
If you are taking magnesium for a specific outcome (sleep, constipation, cramps) rather than general health, the dose and form vary. These ranges are based on clinical practice and the peer-reviewed literature summarised by the NIH Office of Dietary Supplements.
Sleep support
200 to 400 mgForm
Glycinate
Timing
1 to 2 hours before bed
Start at 200 mg, increase only if needed
Anxiety and stress
200 to 400 mgForm
Glycinate
Timing
Split: half morning, half evening
Glycine adds calming effect on top of magnesium
Constipation
200 to 400 mgForm
Citrate
Timing
Morning with water and food
Start at 100 mg, increase only if stool does not soften
Muscle cramps
200 to 400 mgForm
Either
Timing
Consistent daily, with meals
Glycinate if taking at night, citrate if morning
Migraine prevention
400 to 600 mgForm
Either
Timing
Split across 2 to 3 doses
Higher dose range; confirm with your doctor
General deficiency
200 to 300 mgForm
Citrate or glycinate
Timing
With meals
4 to 6 weeks to fully replete stores
Timing and Split Dosing
Why split doses absorb better
The gut absorbs magnesium more efficiently in smaller boluses. A single 400 mg dose is absorbed less completely than two 200 mg doses taken several hours apart. Splitting the dose also reduces the peak GI effect that can cause loose stools or nausea. For most goals, two 150 to 200 mg doses beat one 300 to 400 mg dose.
Morning vs evening
Citrate is better in the morning because its gentle laxative effect is more useful (and less disruptive) during waking hours. Glycinate is better in the evening because glycine supports sleep onset. A common split is citrate at breakfast and glycinate before bed, which covers both digestive and sleep goals.
Consistency beats loading
If you are correcting a deficiency or building up for migraine or cramp prevention, consistent daily dosing over 4 to 6 weeks works better than loading doses. Magnesium is stored primarily in bone and muscle; repletion takes time regardless of dose size.
Upper Limit and Safety
Supplement upper limit: 350 mg per day of elemental magnesium
This UL applies to magnesium from supplements only. Dietary magnesium is not restricted because food intake rarely causes toxicity in people with normal kidney function. Doses above the UL do not usually cause serious harm in healthy adults but are more likely to cause diarrhoea, nausea, and abdominal cramping.
People who should consult a doctor before supplementing
- -Kidney disease or reduced kidney function (magnesium clearance is impaired)
- -Taking antibiotics (tetracyclines, fluoroquinolones), space 2+ hours apart
- -Taking bisphosphonates for osteoporosis, space 2+ hours apart
- -Taking diuretics, magnesium balance may already be altered
- -Pregnant or breastfeeding, confirm the dose and form with your OB
Disclaimer: This content is for educational purposes only and is not medical advice. Before starting any supplement, especially at therapeutic doses or if you have an existing medical condition, consult your healthcare provider.