Last updated: October 2026
Magnesium glycinate, like other forms, mostly leaves your system within a day or two. It’s absorbed over several hours, healthy kidneys pass out what you don’t need in your urine, and anything unabsorbed leaves in your stools. There’s no reliable half-life for it, and the magnesium stored in bones and muscles builds up over weeks.
Below: the glycinate and half-life questions, what happens to a dose hour by hour, differences between forms, whether magnesium builds up, how long it takes to work, and how to get magnesium out of your system if you’ve taken too much. Sources checked October 2026.
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View productHow long does magnesium glycinate stay in your system?
About the same as any other well-absorbed form: most of a dose is absorbed or passed within a day or two. Glycinate (bisglycinate) is magnesium bound to the amino acid glycine. What sets it apart is how it’s absorbed, not how long it stays:
- It may be absorbed a little sooner. In a small 1994 trial of 12 people who’d had part of their small intestine removed, absorption peaked about 3 hours earlier with a magnesium glycinate chelate than with magnesium oxide. The researchers thought some glycinate is absorbed intact, by the route the gut uses for small protein fragments.
- Less rushes straight through. Glycinate was better tolerated than oxide in that trial, and it’s less likely to loosen stools than citrate or oxide, so less magnesium leaves unabsorbed.
- Once absorbed, it’s simply magnesium. Your kidneys pass out what you don’t need, and the rest goes to bones, muscles and other tissues.
Magnesium glycinate half-life: is there one?
Not a reliable one. We couldn’t find a human study that measured a half-life for magnesium glycinate taken by mouth, so treat the “8 to 9 hours” figures you’ll see online with caution. Your body keeps blood magnesium in a tight range, so a single half-life doesn’t describe it well anyway.
The closest real measurement comes from 20 hospital patients after heart surgery, given about 490mg of magnesium (20 mmol) straight into a vein. Their blood levels peaked within an hour and were close to where they started by 12 hours, and about 95% of the dose turned up in their urine over those 12 hours. Swallowed magnesium arrives more slowly, over several hours, so expect the excess from a supplement to take a little longer, typically about a day.
Your stores are different: magnesium in bone and muscle is topped up over weeks, so daily use matters more than timing. If your kidneys don’t work well, magnesium can build up (see magnesium and your kidneys).
What happens to a dose of magnesium
| Stage | What happens | Roughly when |
|---|---|---|
| Absorption | Somewhere between about a quarter and three-quarters of the magnesium you take in is absorbed, mostly in the small intestine. The lower your levels, the more you absorb. | Over several hours |
| In the blood | Only about 1% of your body’s magnesium is outside your cells, and just 0.3% is in your blood serum. Blood levels are kept within a tight range. | Constantly balanced |
| Into tissues | About 99% of your magnesium is in bones, muscles and soft tissues, with roughly 50 to 60% in bone. | Builds up over weeks |
| Kidneys | The kidneys filter about 2,400mg of magnesium a day and immediately reabsorb about 95%, so only around 100mg leaves in urine. They can raise or lower this quickly depending on how much you take in. | Excess passed out quickly, mostly at night |
| Unabsorbed magnesium | Leaves in your stools, and can loosen them. | With your next bowel movements |
An adult body holds roughly 24g of magnesium in total, so a single 150mg supplement is a small top-up rather than a big change.
Stocking up for winter? Our Black Friday supplement deals run from 27 to 30 November.
If you take citrate, our magnesium citrate guide covers dose, timing and side effects.
How much water should you drink a day? Our guide gives the NHS guidance and simple signs you are getting enough.
Curious about the L-theanine in our blend? Our guide to L-theanine benefits covers what the research shows and how much people take.
The FSA’s 10mg a day figure for CBD is precautionary advice rather than a legal limit, set while longer-term safety research continues. At Evopure we think it is a very cautious figure, and many adults use more. If you go above it, increase slowly, and check with your GP or pharmacist first if you take any medication.
Glycinate, citrate, oxide, taurate and threonate
| Form | How long it stays | Notes |
|---|---|---|
| Glycinate (bisglycinate) | Mostly absorbed or passed within a day or two, like other forms | Well tolerated; less laxative effect, so less passes straight through |
| Citrate | Same once absorbed | Well absorbed; more of a laxative effect at higher doses |
| Oxide | Much is unabsorbed and leaves in stools within 1 to 3 days | Lower absorption; often used as a laxative |
| Taurate | Same once absorbed | Little research specific to this form |
| L-threonate | Same once absorbed | Low magnesium content per capsule. See magnesium L-threonate. |
Once magnesium is absorbed, your body handles it the same way whatever form it came from. The form mainly affects how much is absorbed and how your gut tolerates it. See types of magnesium.
Comparing brands and forms? Our best magnesium supplement UK guide sets out what to look for on the label, form by form.
Does magnesium build up in your system?
Yes, slowly, if you were low to begin with. Stores in bones and muscles are topped up over weeks of regular intake, not from a single dose. If you’re already well supplied, your kidneys simply pass out the extra. That’s why trials usually run for 4 to 8 weeks, and why taking magnesium daily matters more than the exact time.
How long does magnesium take to work?
- Laxative effect: hours to a day or two. See magnesium for constipation.
- Evening routine and sleep: many people give it two to four weeks. See magnesium for sleep.
- Correcting a low intake: several weeks of daily use.
Full timeline: how long magnesium takes to work. Magnesium contributes to a reduction of tiredness and fatigue and to normal muscle function.
Taking magnesium for tiredness? Our guide to the best supplements for energy compares it with iron, B vitamins and vitamin D.
Magnesium in your body: a timeline
| Time after you start | What’s going on |
|---|---|
| First few hours | The dose is absorbed through the small intestine |
| Same day and night | Blood levels stay steady; your kidneys pass out what you don’t need, with most excretion at night |
| Next bowel movements | Unabsorbed magnesium leaves in your stools, which is why high doses can loosen them |
| 2 to 8 weeks of daily use | If you were low, stores in bone and muscle are gradually topped up. Most trials ran for this long |
| After you stop | Your body keeps drawing on its stores and adjusts how much it absorbs and excretes, so levels don’t crash overnight |
What makes you lose magnesium faster?
Some things increase how much magnesium you lose, or reduce how much you absorb. A medical review lists:
- Long-lasting or severe diarrhoea.
- Some medicines, including loop diuretics (water tablets such as furosemide) and proton pump inhibitors such as omeprazole. The MHRA has warned that long-term PPI use, especially for over a year, can cause low magnesium.
- Heavy drinking over a long time.
- Diabetes.
- Prolonged exercise, heat and heavy sweating.
iIf any of these apply and you have symptoms such as cramps, twitching or tiredness, speak to your GP or pharmacist. Don’t stop prescribed medicine on your own. See signs of magnesium deficiency and electrolytes.
Magnesium sprays and Epsom salt baths: how much gets in?
Probably very little. A 2017 review of the evidence concluded that the idea of magnesium being absorbed through the skin from sprays, flakes or bath salts is scientifically unsupported. A warm bath or massage can still be a relaxing part of an evening routine, but if you want to top up your magnesium, food and oral supplements are the proven routes. See magnesium spray.
Do you need to take magnesium every day?
Because excess is passed out quickly and stores change slowly, steady daily intake works better than occasional large doses. Spreading larger amounts across the day can also be gentler on your gut. The NHS says adults need 300mg (men) or 270mg (women) a day, most of which can come from food such as spinach, nuts and wholemeal bread, and 400mg or less a day from supplements is unlikely to cause harm. See foods high in magnesium and the best time to take magnesium.
Our Magnesium Glycinate Sleep Complex is a daily berry evening drink with magnesium bisglycinate and citrate plus L-theanine. Magnesium contributes to a reduction of tiredness and fatigue and to normal muscle function.
How to get magnesium out of your system if you’ve taken too much
For most healthy people, the first sign of too much magnesium from supplements is diarrhoea, and it settles once you stop. Healthy kidneys pass most of the extra out in urine within about a day. The NHS says 400mg or less a day from supplements is unlikely to cause harm.
- Stop or reduce the supplement and any magnesium-containing laxatives or antacids.
- Drink fluids to replace what you lose through diarrhoea.
- Let your kidneys do the work: healthy kidneys can quickly increase how much magnesium they pass out.
Dangerously high magnesium levels are rare and usually happen in people with kidney disease, or after very large doses of magnesium laxatives or Epsom salts. Call 111, or 999 in an emergency, if someone has taken a large amount and has drowsiness, weakness, low blood pressure, slow heartbeat, confusion or difficulty breathing. Hospitals can treat it. There’s no safe home “detox” for high magnesium.
Can a blood test tell how much you have?
Only partly. A standard blood test measures the small amount of magnesium in your blood, which your body keeps steady by drawing on stores. So a normal result doesn’t rule out low stores. Your GP will consider your symptoms, diet and medicines too. See signs of magnesium deficiency.
Magnesium and your kidneys
Your kidneys are what stop magnesium building up, so kidney health matters most for safety. If you have kidney disease, don’t take magnesium supplements, magnesium laxatives or antacids unless your doctor advises it, because your body can’t clear the excess properly. The same applies to Epsom salts taken by mouth or as an enema, which have caused dangerous magnesium levels.
See also Epsom salt bath benefits and how to use them.
Healthy kidneys clear extra magnesium, but if yours don’t, read about high blood magnesium and kidney disease.
Related guides
- Absorption differs by form; see which magnesium is absorbed best: glycinate, citrate or threonate.
- For dose, timing and side effects of the most popular form, see our guide to magnesium glycinate.
- Taking it as a drink? Our guide to magnesium powder covers forms, label checks and how to use it.
Sources 7
- Jahnen-Dechent W, Ketteler M. Magnesium basics. Clin Kidney J, 2012.
- de Baaij JH et al. Magnesium in man: implications for health and disease. Physiol Rev, 2015.
- NHS. Vitamins and minerals: magnesium.
- Schuette SA et al (1994). Bioavailability of magnesium diglycinate vs magnesium oxide in patients with ileal resection. JPEN J Parenter Enteral Nutr. PMID 7815675.
- Biesenbach P et al (2018). Pharmacokinetics of magnesium bolus therapy in cardiothoracic surgery. J Cardiothorac Vasc Anesth. PMID 29169799.
- Gröber U et al (2017). Myth or reality: transdermal magnesium? Nutrients.
- MHRA (2012). Proton pump inhibitors in long-term use: reports of hypomagnesaemia. Drug Safety Update.
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
