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The tolerable upper intake level (UL), or upper limit, for magnesium is 350 mg a day for everyone 9 and older. That is the most a day that is unlikely to cause harm for almost everyone; above it, the chance of side effects goes up. It is a ceiling, not a target. The limit counts only magnesium from supplements and medicines, not the magnesium in food and water. That’s why it is lower than the 420 mg a day men need in total (320 mg for women).
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Servings a day
This limit is the same for everyone 9 and older, including pregnancy and breastfeeding.
Type the amount from your label to compare it with the upper limit.
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Magnesium upper limits by age
| Age | Males | Females | Pregnancy | Breastfeeding |
|---|---|---|---|---|
| Birth to 6 months | Not set | Not set | – | – |
| 7-12 months | Not set | Not set | – | – |
| 1-3 years | 65 mg | 65 mg | – | – |
| 4-8 years | 110 mg | 110 mg | – | – |
| 9-13 years | 350 mg | 350 mg | – | – |
| 14-18 years | 350 mg | 350 mg | 350 mg | 350 mg |
| 19-30 years | 350 mg | 350 mg | 350 mg | 350 mg |
| 31-50 years | 350 mg | 350 mg | 350 mg | 350 mg |
| 51-70 years | 350 mg | 350 mg | – | – |
| 71+ years | 350 mg | 350 mg | – | – |
No upper limit could be set for babies; the National Academies say their intake should come from food and formula only.
How much Magnesium you need
| Age | Males | Females | Pregnancy | Breastfeeding |
|---|---|---|---|---|
| Birth to 6 months | 30 mg* | 30 mg* | – | – |
| 7-12 months | 75 mg* | 75 mg* | – | – |
| 1-3 years | 80 mg | 80 mg | – | – |
| 4-8 years | 130 mg | 130 mg | – | – |
| 9-13 years | 240 mg | 240 mg | – | – |
| 14-18 years | 410 mg | 360 mg | 400 mg | 360 mg |
| 19-30 years | 400 mg | 310 mg | 350 mg | 310 mg |
| 31-50 years | 420 mg | 320 mg | 360 mg | 320 mg |
| 51-70 years | 420 mg | 320 mg | – | – |
| 71+ years | 420 mg | 320 mg | – | – |
* Adequate Intake (AI): the amount set when there isn’t enough evidence for an RDA.
What counts toward the Magnesium limit
The limit counts only magnesium from supplements and medicines, not the magnesium in food and water.
What happens with too much Magnesium
The 1997 National Academies report (Ch. 6, pp. 243-244) says "The primary initial manifestation of excessive magnesium intake from nonfood sources is diarrhea". It says this "may be accompanied by other mild gastrointestinal effects such as nausea and abdominal cramping". It adds that "Hypermagnesemia can occur in individuals with impaired renal function" and can "result in more serious neurological and cardiac symptoms". The report says magnesium that occurs naturally in food has not been shown to cause adverse effects.
Sources: Health Canada, Dietary Reference Intakes tables (the joint U.S.-Canada values); National Academies, Dietary Reference Intakes for Calcium and Vitamin D (2011); National Academies, Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (1997). Limits checked November 8, 2026. More from the NIH: Office of Dietary Supplements Magnesium fact sheet.
If you think you or a child took too much of a supplement, call Poison Control at 1-800-222-1222 (U.S., free, 24 hours) or use poison.org. In an emergency, call 911.
General information, not medical advice. Your doctor may recommend a different amount, for example to treat a deficiency. Talk to your doctor or pharmacist before you start, stop or change a supplement, especially if you are pregnant, nursing, take medication or have a medical condition.