mineral
Evidence tier: limited
Magnesium is a foundational mineral required for over 300 enzymatic processes in the body, including GABA synthesis (for sleep and calm), muscle relaxation, and nervous system regulation. Most Western diets fall short.
Magnesium is a cofactor in more than 300 enzyme systems and is needed for muscle and nerve function, blood sugar and blood pressure regulation, and bone. In the nervous system it sits in the NMDA receptor channel and damps excitatory signalling. Unabsorbed magnesium salts draw water into the bowel, which is why higher doses loosen stools.
An essential mineral with a thin therapeutic file, and the form question has honest answers. About 48 percent of Americans eat less than the estimated requirement (NIH ODS), so the real case is filling a common gap. Sleep: limited (3 small trials in 151 older adults, sleep onset about 17 minutes faster, low to very low quality, PMID 33865376; one bisglycinate trial at 250 mg found a small effect, PMID 40918053). Anxiety: suggestive but poor quality (PMID 28445426). Night cramps: Cochrane says unlikely to help older adults (PMID 32956536). Blood pressure: a 3 to 4 mmHg systolic fall in a meta analysis of 22 trials (NIH ODS). Migraine: probably effective by neurology guidelines, but the dose exceeds the upper limit, so medical supervision only. Constipation: moderate evidence, for magnesium oxide only, at 0.5 to 1.5 g a day (PMID 37243443, BDA 2025 PMID 41081513). Forms: citrate is among the better absorbed (NIH ODS); glycinate is not ranked by ODS, is not on its list of forms that most often cause diarrhoea, and has the one form specific sleep trial; oxide is poorly absorbed and the constipation form; L-threonate and taurate have no human outcome trials that change this picture. Limits: 350 mg a day from supplements (US), 400 mg or less unlikely to harm (NHS), 250 mg (EFSA). The one hard stop is kidney disease.
200 to 350 mg of elemental magnesium a day. The US upper limit is 350 mg a day from supplements, including in pregnancy and breastfeeding; the NHS says 400 mg or less is unlikely to harm; the EU limit is 250 mg. Constipation doses of oxide (0.5 to 1.5 g of compound) go above these and need a pharmacist or doctor.
Always read the elemental magnesium figure, not the compound weight: 250 mg elemental is about 415 mg of oxide, 1,550 mg of anhydrous citrate, 1,770 mg of pure bisglycinate or 3,000 mg of L-threonate. Keep total supplemental magnesium at 350 mg a day or less (US); the UK NHS says 400 mg or less is unlikely to harm and the EU limit is 250 mg. Which form: citrate for absorption (NIH ODS ranks it among the better absorbed), glycinate as a gentle option with the one form specific sleep trial, oxide only for constipation. Space from antibiotics (tetracyclines and quinolones 2 hours before or 4 to 6 hours after), bisphosphonates (2 hours) and levothyroxine (4 hours). Not with kidney disease unless a doctor advises. [NIH ODS; NHS; EFSA; claims register MAG-11, MAG-12]
Onset: ~28 days
Safe within tolerable upper intake levels. Upper tolerable intake from supplements: 350 mg elemental Mg/day (adults). Excess causes osmotic diarrhoea, a key side effect differentiating forms. Glycinate and threonate cause least GI upset. Citrate is moderate; oxide has highest laxative effect. Renal impairment: do not supplement without medical supervision, magnesium is renally cleared and can accumulate dangerously in kidney disease.
Pregnancy: safe
Breastfeeding: safe
Not a traditional botanical remedy, magnesium is an essential mineral. Epsom salt baths (magnesium sulphate) have been used for muscle relaxation and nervous system support in folk medicine since the 17th century. One of the most widely researched minerals for sleep and stress.
Active compounds: elemental magnesium, magnesium bisglycinate
Remedies using Magnesium · Browse by body system · Check it against what you take
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.