If you've ever tried magnesium and felt nothing, you're not broken. The supplement probably was.
Magnesium is one of the most important minerals in the human body. It's involved in over 300 enzymatic reactions — muscle function, nervous system regulation, sleep quality, blood sugar, blood pressure, and energy production. Most adults don't get enough of it from food alone. So people supplement. And most of them use the wrong form.
The cheap form problem.
Walk into any drugstore and the magnesium on the shelf is almost always magnesium oxide. It's cheap, it's shelf-stable, and it's absorbed at roughly 4%. That means if you take a 500mg capsule of magnesium oxide, your body might actually use around 20mg of it. The rest passes through you — which is also why high doses of oxide tend to send people running to the bathroom.
Magnesium citrate is a step up. Better absorbed, gentler on the gut, but still primarily used for its laxative effect.
The form that actually does something.
Magnesium glycinate is magnesium bound to glycine, a calming amino acid. It's absorbed well, it's gentle on the stomach, and the glycine itself supports relaxation and sleep. This is the form used in most of the clinical studies people cite when they talk about magnesium for anxiety, sleep, and recovery.
The dose matters as much as the form.
The recommended daily intake for adults sits around 310–420mg of elemental magnesium, depending on age and sex. A lot of supplements list the weight of the compound on the front (say, "1,000mg magnesium glycinate") but only contain a small fraction of actual elemental magnesium. Always check the elemental amount on the supplement facts panel.
The bottom line.
If you're going to take magnesium, take a form your body can use, at a dose that matches the research. Otherwise you're just paying for an expensive trip to the bathroom.