Ghost Fitness/Magnesium/What are the side effects of taking magnesium tablets?
What are the side effects of taking magnesium tablets?
The short answer
The side effects are the salt's: tablets are usually magnesium oxide, the least absorbed and most laxative salt, so loose stools are the common tablet complaint, plus nausea when fasted. The tablet adds two of its own, a large size to swallow and slower disintegration. A bisglycinate capsule sidesteps all four.
- Why tablets mean oxideoxide is about 60% magnesium: a full 375mg fits one pressed tablet cheaply
- The oxide side effectleast absorbed, most laxative: loose stools at a reference-value dose
- The tablet's own issuesa large pressed tablet to swallow; slower disintegration than a capsule
- The alternativebisglycinate in capsules: best absorbed, least laxative, no pressing
Our brand: the worked example on this page
Futuro Labs Magnesium Glycinate
- 22p a day
- 180 capsules, 2 capsules daily
- Lab tested
- Made in the UK
The capsule that sidesteps the tablet's problems: Futuro Labs Magnesium Glycinate on Amazon UK, bisglycinate in HPMC capsules, 300mg elemental at 80% NRV, £19.99 for 90 days at 22p. Full label breakdown. The tablets-or-capsules comparison is on the buying-tablets page; the salt comparison on the forms page.
The side effects are the salt's, and why a magnesium tablet is so often an oxide tablet
The side effects of taking magnesium tablets are the side effects of whatever salt the tablet contains, because a tablet is a format and not an ingredient, and the reason the question is asked about tablets specifically is that tablets so often mean oxide. Magnesium oxide is about 60% magnesium by weight, the most concentrated of the common salts, so a full 375mg reference value fits into one pressed tablet cheaply, which is why the supermarket, pharmacy own-brand and multi-formula tablets that most people mean by magnesium tablets are oxide or an oxide-led blend, the type page's pattern, whereas bisglycinate at around 20% magnesium needs two or three capsules and is rarely pressed into a tablet at all. Oxide's side effects follow: it is the least absorbed salt in the comparative trials, so a large fraction of a tablet's magnesium stays in the gut, and the most laxative for the same reason, unabsorbed magnesium drawing water into the bowel, so loose stools at a reference-value dose are the common magnesium-tablet complaint, worse fasted, worse at night, and the reason the buying-tablets page's verdict is decided by salt rather than by format. The fasted nausea a minority of people get from any mineral applies to tablets as to capsules, fixed by a meal. A magnesium tablet that is citrate has citrate's moderate laxative effect, and a tablet that is a chelate, rarer and larger, has the chelate's tolerance, the salt on the ingredients list deciding the side effect every time.
The two issues that belong to the tablet itself, the alternative, and the side effects filed
Two issues belong to the tablet format itself rather than to its salt. Size: a pressed tablet delivering a full reference value of any salt with its binders, disintegrants and coating is large, oxide tablets often being the size that some people struggle to swallow, and a coating that eases swallowing can add the titanium dioxide the other-ingredients guide notes, so a reader who finds magnesium tablets hard to take has a mechanical problem that splitting the tablet, taking it with a full glass of water and a meal, or changing to capsules solves. Disintegration: a pressed tablet must break apart in the stomach before its salt dissolves, and tablets disintegrate more slowly and less predictably than capsules, whose shells dissolve in minutes, so a poorly made tablet can pass partly intact and deliver less than its label, the buying-tablets page's note and a reason a tablet's certificate of analysis for disintegration matters where a brand offers one. The alternative sidesteps all four: bisglycinate, the best-absorbed and least laxative salt, in capsules, which need no pressing, no binders and no coating and dissolve in minutes, at a dose under the guidance level with the evening meal, the worked example's format, two HPMC capsules delivering 300mg elemental at 80% NRV, £19.99 for 90 days at 22p. The side effects filed: loose stools from oxide's poor absorption, nausea when fasted, a large tablet to swallow and slower disintegration, the first two the salt's and the last two the tablet's, and none of them a feature of a bisglycinate capsule taken with dinner.
| The side effect | Whose it is | The fix |
|---|---|---|
| Loose stools | The salt: oxide, least absorbed and most laxative | A better-absorbed salt; a lower dose |
| Nausea when fasted | Any mineral, in a minority | A meal |
| Hard to swallow | The tablet: a large pressed dose with binders and coating | Water, a meal, splitting, or capsules |
| Slower disintegration | The tablet: must break apart before dissolving | Capsules dissolve in minutes |
| Why tablets mean oxide | 60% magnesium fits one tablet cheaply | Read the ingredients list |
| The alternative | Bisglycinate capsules | Sidesteps all four |
The verdict, the salt's side effects in a format that adds two
What are the side effects of taking magnesium tablets: the salt's above all, tablets so often being oxide because 60% magnesium fits a reference value into one pressed tablet cheaply, oxide being the least absorbed and most laxative salt so that loose stools are the common tablet complaint, with fasted nausea as any mineral's, and two issues that belong to the tablet itself, a large dose to swallow and slower, less predictable disintegration than a capsule. The capsule that sidesteps all four: Futuro Labs Magnesium Glycinate, bisglycinate in HPMC capsules, 300mg elemental at 80% NRV with the evening meal, £19.99 for 90 days at 22p a day.
What to check on the label
- Read the salt, not the format: the side effects are the salt's.
- Expect oxide in a tablet: and its loose stools.
- Take any tablet with a meal and water: nausea and swallowing.
- Know the disintegration issue: tablets must break apart first.
- Change to bisglycinate capsules: all four problems gone.
Our brand
The worked example: Futuro Labs Magnesium Glycinate
Futuro Labs Magnesium Glycinate is the worked example for magnesium reviews because its label states every number a review needs: 1500mg magnesium bisglycinate at 20%, 300mg elemental, 80% NRV, 2 capsules a day, 180 capsules for £19.99, 22p a day, UK made, vegan HPMC shell, batch tested for lead, mercury, arsenic and cadmium, and only the register's own magnesium claims printed.
- Elemental magnesium per serving
- 300mg (80% NRV)
- Form
- magnesium bisglycinate 20%
- Serving
- 2 capsules a day
- Bottle
- 180 capsules, 90 days
- Price
- £19.99 (22p a day)
- Capsule
- vegetarian shell, vegan product
Questions people also ask
Why do magnesium tablets give me diarrhoea?
Because most magnesium tablets are magnesium oxide, the least absorbed and most laxative salt, chosen because 60% magnesium fits a full reference value into one cheap tablet, and its unabsorbed fraction draws water into the bowel.
Are magnesium tablets worse than capsules for side effects?
Usually, because of the salt: tablets tend to be oxide and capsules tend to be bisglycinate or citrate, and the tablet format adds a large size to swallow and slower disintegration of its own.
Why are magnesium tablets so big?
A pressed tablet delivering a full reference value carries the salt plus binders, disintegrants and a coating, so an oxide tablet at 375mg elemental is large; splitting it, taking it with water and a meal, or changing to capsules solves the swallowing.
Do magnesium tablets absorb properly?
Less reliably than capsules: a tablet must disintegrate in the stomach before its salt dissolves, which is slower and less predictable than a capsule shell dissolving in minutes, and a poorly made tablet can pass partly intact.
What is the best alternative to magnesium tablets?
Bisglycinate in capsules: the best-absorbed and least laxative salt in a format that needs no pressing, binders or coating and dissolves in minutes, at 300mg elemental with the evening meal.
Sources
- Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnesium Research 2001;14(4):257-262. PubMed record
- Walker AF, Marakis G, Christie S, Byng M. Mg citrate found more bioavailable than other Mg preparations in a randomised, double-blind study. Magnesium Research 2003;16(3):183-191. PubMed record
- The GB claims register, magnesium entries: magnesium contributes to a reduction of tiredness and fatigue, normal psychological function, normal nervous system function, normal muscle function and electrolyte balance, among others. https://www.gov.uk/government/publications/great-britain-nutrition-and-health-claims-nhc-register
- Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals. Food Standards Agency, 2003 (magnesium guidance level 400mg a day from supplements). https://cot.food.gov.uk/sites/default/files/vitmin2003.pdf