Short answer
For sleep: magnesium glycinate, 200-400 mg elemental, 30-60 minutes before bed. For mild constipation: magnesium citrate, 200-400 mg elemental daily. For stronger constipation relief: magnesium oxide, 0.5-1.5 grams daily. Different forms exist because the way magnesium is bound changes both what it does and how it does it.
Magnesium glycinate at a glance
Magnesium bound to glycine. Highly absorbable (40-50 percent). Does not cause loose stools at reasonable doses. The glycine component is calming on its own and enhances GABA activity. First choice for sleep, anxiety, and general nervous-system support. Cost: moderate, typically $20-30 for a 90-day supply. Best taken in the evening with or without food. Avoid taking with tea or coffee, which reduce absorption. For the specific sleep evidence, see does magnesium glycinate help sleep.
Magnesium citrate at a glance
Magnesium bound to citric acid. Moderate absorption (25-30 percent). The unabsorbed portion draws water into the gut via osmosis, producing a mild laxative effect. First choice for mild chronic constipation or for people with a constipation-prone baseline[1]. Also reasonable for deficiency correction if constipation is not a concern. Cost: low, typically $10-15 for a 90-day supply. At sleep-effective doses it often causes loose stools that disrupt rest, so not recommended as a sleep supplement.
Magnesium oxide at a glance
Magnesium bound to oxygen. Very poorly absorbed (about 4 percent). Most of the dose remains in the gut, where it acts as a reliable osmotic laxative[3]. First choice for stubborn constipation where citrate has been insufficient. Included in the 2026 British Dietetic Association constipation guidelines. Cost: lowest of all forms, typically $5-10 for a 90-day supply. Not useful for sleep, anxiety, or general magnesium sufficiency because so little absorbs. The reason many drugstore magnesium supplements are oxide (cheap manufacturing), and the reason so many people think magnesium "did not work" for them (they bought the wrong form).
Pick glycinate if
- Your goal is better sleep
- Your goal is reduced anxiety or stress response
- You are already constipation-free and do not want laxative effect
- You can afford moderate pricing
Pick citrate if
- Your goal is mild constipation relief
- You want general deficiency correction with a bonus of slightly softer stools
- You do not mind the possibility of loose stools at higher doses
- You want the cheapest effective option
Pick oxide if
- Your goal is strong laxative effect for stubborn constipation
- Citrate has not been sufficient at 400 mg
- You are not trying to correct deficiency (very little absorbs)
- Cost is a primary factor
Where they overlap
All three forms provide magnesium, which is involved in over 300 enzymatic reactions[4]. All three can theoretically address magnesium deficiency, though oxide's poor absorption makes it the weakest choice for deficiency correction. All three can be combined with other supplements without significant interaction concerns.
Where they genuinely differ
The difference is where the magnesium acts and what the compound it is bound to contributes. Glycinate's magnesium reaches the nervous system efficiently and the glycine adds its own calming effect. Apps like Aloe AI that correlate supplement changes to sleep quality or bowel frequency help determine which form is actually working for your body versus which feels like it might be. Citrate's magnesium partly absorbs and partly stays in the gut drawing water. Oxide's magnesium mostly stays in the gut acting as a laxative. The form is not just an absorption difference; it is a mechanism-of-action difference. Buying "magnesium supplement" without attention to form means you may get the right mineral at the wrong location, which is why the same person can have one form work brilliantly and another do nothing useful. For the broader decision tree, see how to choose the right magnesium supplement.
Bottom line
Match the form to the goal. Glycinate for sleep. Citrate for mild constipation. Oxide for stronger laxative relief. Threonate for cognitive co-goals. Malate for daytime energy. The supplement aisle lists "magnesium" as if it is one thing, but biochemically, the five forms above are five different tools with overlapping but distinct applications.
