This is a good question, since magnesium can make up less than half the weight of compounds which include it, such as magnesium citrate, magnesium chloride, and magnesium glycinate.
The amount of actual magnesium (sometimes listed as "elemental magnesium) you are getting from your supplement should
be indicated on the label, but that's not always the case, so it's important to notice how
the information is stated. For example, if your supplement label states: "Magnesium (as magnesium citrate)....500 mg" it should contain 500 mg of actual magnesium. However, if the label says "Magnesium citrate 500 mg," this means the entire compound is 500 mg — of which only a small percentage is magnesium (in fact, it's only 16.2%). Also, remember that even when a supplement appears to be properly labeled, the only way to know for sure whether it contains what it claims is if it has been tested by an independent group like ConsumerLab.com. Not all products contain what they claim.
For more about how to read magnesium supplement labels, including an example of a misleading label
from a product reviewed by ConsumerLab.com, see the Magnesium Supplements Review >>
(The Review includes the results of our latest product tests and information about what magnesium does, proper dosage, side effects, and how the forms of magnesium differ.)
Note that this labeling rule applies to other essential minerals, such as calcium
. See the "ConsumerTips" section of our Reviews of supplements made from each for more about the different forms and what to look for on labels.
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Learn More About Magnesium Supplements:
Which is the best form of magnesium to take - one that contains the most magnesium and is best absorbed? >>
How can the Recommended Daily Allowance (RDA) for magnesium be higher than the Upper Tolerable Intake Level (UL)? That is, how can an amount which is healthful also put you at risk for harm? >>
Is it important to take calcium and magnesium together? >>
Is it true that I should not keep magnesium supplements in a daily pill pack mixed with other supplements and medicines? >>
Is there an accurate test for magnesium deficiency? >>
Are there drug interactions with magnesium supplements? >>