Magnesium citrate works by attracting water through the tissues by a process known as osmosis. Once in the intestine, it can attract enough water into the intestine to induce defecation. The additional water stimulates bowel motility. This means it can also be used to treat rectal and colon problems. Magnesium citrate functions best on an empty stomach, and should always be followed with a full (eight ounce) glass of water or juice to help the magnesium citrate absorb properly and help prevent any complications. Magnesium citrate is generally not a harmful substance, but care should be taken by consulting a health-care professional if any adverse health problems are suspected or experienced.
The maximum Upper Tolerable Limit for magnesium in supplement form for adults is 350 mg per day of elemental magnesium according to the National Institutes of Health (NIH). In addition, according to the NIH, total dietary requirements for magnesium from all sources (i.e. food and supplements) is 320–420 mg of elemental magnesium per day, though there is no upper tolerance limit (UTL) for dietary Magnesium.
As a laxative syrup with a concentration of 1.745 g of magnesium citrate per fl. oz, a typical dose for adults and children twelve years or older is between 7 and 10 US fluid ounces (210 and 300 ml; 7.3 and 10.4 imp fl oz), followed immediately with a full 8 US fluid ounces (240 ml; 8.3 imp fl oz) glass of water. Consuming an adult dose of 10 oz of laxative syrup (@ 1.745 g/oz) implies a consumption of 17.45 g of magnesium citrate in a single 10 oz dose resulting in a consumption of approximately 2.0 g of elemental magnesium per single dose. Given that this laxative dose contains five times the recommended nutritional dose for magnesium, caution should be taken to avoid prolonged usage (i.e. over five days) and to follow the manufacturer's instructions strictly. For children between three and twelve years of age, the typical dose is roughly half that, based on physician recommendation. Magnesium citrate is not recommended for use in children and infants two years of age or less.
Although less common, as a magnesium supplement the citrate form is sometimes used because it is believed to be more bio-available than other common pill forms, such as magnesium oxide. However, according to one study, magnesium gluconate is marginally more bio-available than magnesium citrate.
Magnesium citrate, as a supplement in pill form, is useful for the prevention of kidney stones.
It is always important to correctly follow the prescribed doses; extreme magnesium overdose can result in serious complication such as slow heart beat, low blood pressure, nausea, drowsiness, etc. If severe enough, an overdose can even result in coma or death. However, a moderate overdose will be excreted through the kidneys, unless one suffers from serious kidney problems.
Magnesium citrate solutions generally produce bowel movement in one half to six hours. Rectal bleeding or failure to have a bowel movement after use could be signs of a serious condition.
^Coudray, C; Rambeau, M; Feillet-Coudray, C; Gueux, E; Tressol, JC; Mazur, A; Rayssiguier, Y (December 2005). "Study of magnesium bioavailability from ten organic and inorganic Mg salts in Mg-depleted rats using a stable isotope approach". Magnes Res18 (4): 215–23. PMID16548135.
^Ettinger, B; Pak, CY; Citron, JT; Thomas, C; Adams-Huet, B; Vangessel, A (December 1997). "Potassium-magnesium citrate is an effective prophylaxis against recurrent calcium oxalate nephrolithiasis". J Urol158 (6): 2069–73. doi:10.1016/S0022-5347(01)68155-2. PMID9366314.