Magnesium is a popular bedtime supplement, but the evidence for improving sleep is limited. A few small trials, mostly in older adults, suggest it may help people fall asleep a little faster or sleep slightly better. Study quality is generally low, and people who already get enough magnesium from food are unlikely to notice much.

The form does matter, mainly for absorption and side effects:

  • Magnesium glycinate: Well tolerated and gentle on the stomach. A common choice for sleep, though sleep-specific evidence is thin.
  • Magnesium citrate: Well absorbed but has a laxative effect at higher doses.
  • Magnesium oxide: Cheap and high in elemental magnesium, but poorly absorbed and the most likely to upset the gut.
  • Magnesium threonate: Marketed for brain benefits, but human data is very limited.

Stick to the dose on the label. The NHMRC upper level for supplemental magnesium is 350 mg per day for adults. People with kidney disease should not take magnesium supplements without medical advice, and it can interact with some antibiotics and osteoporosis medications.

If sleep is a persistent problem, the best-supported fixes are consistent sleep and wake times, limiting caffeine and screens, and cognitive behavioural therapy for insomnia (CBT-I).

Bottom line: Magnesium may help some people. Pick a well-tolerated form and don’t expect a cure for poor sleep habits.