Not all magnesium is the same, and the difference matters more than the label suggests. Magnesium comes in several forms, each suited to a different job in the body.
Magnesium glycinate - the form used here - is bound to glycine, an amino acid that's itself calming to the nervous system. It's genuinely the form most often chosen for sleep specifically, and there's a real reason beyond marketing: research on patients with impaired magnesium absorption found the glycinate form was taken up more efficiently than magnesium oxide, particularly in those with the greatest absorption difficulty (Schuette et al., 1994). It's also consistently reported as gentler on the stomach than other common forms.
That's worth knowing, because not every magnesium is interchangeable. Magnesium oxide - the cheapest, most common form on pharmacy shelves - has comparatively poor absorption, which is part of why it's more often used as an antacid or mild laxative than for sleep support. Magnesium citrate has a similar bowel-moving effect, which is exactly why it's a common ingredient in laxative products. Other forms are built for entirely different purposes: magnesium taurate is generally associated with cardiovascular support, magnesium malate with energy metabolism and muscle comfort, and magnesium chloride is mostly used topically - as an oil or bath flakes - rather than taken orally.
Most people don't get enough magnesium in the first place. NIH data from a national U.S. health survey found that roughly 48% of Americans take in less magnesium from food alone than recommended - a genuinely common shortfall, not a rare one. Everyday habits many people already have - caffeine, alcohol, ongoing stress - all place extra demand on magnesium levels, which is part of why an evening dose can feel less like adding something new, and more like removing a quiet obstacle that was already there.