There are two types of magnesium supplement...
1)inorganic salts
2)organic chelates.

Inorganic salts include epsom salts (magnesium sulfate), magnesium chloride
as found in delayed release forms SlowMag, and its generic equivs MagDelay and Mag64.
And Magnesium Oxide (which time has proven in studies to be next to useless).

The chelates are citrate, lactate, glycinate, malate, taurate..these are the most common. This is magnesium bonded to an amino acid which then allows for better absorption with less stool loosening (a common side effect).

Recent studies have shown that not all magnesium supplements are bioavailable --meaning absorbed well from the GI tract.

Magnesium lactate is the best, most completely absorbed.
Magneisum oxide is the worst, by far, and should be avoided.

The rest provide in intermediate level of success and if you want dual effects, some of the chelates afford those. Magnesium taurate provides taurine, which some Tourette's patients do well on. Taurine is also good for the heart.
Magnesium malate provides malic acid which Fibromyalgia patients often find helpful. Anyone with muscle issues would find this useful.
Magnesium citrate can be very laxative, but some people find this useful if they have chronic constipation.

For many, foods offer a safe and easy way to get enough magnesium. This is best for children, and I prefer this way myself. The Linus Pauling site I posted above gives good food choices to do it this way. It also provides dosing suggestions. When taking a supplement of magnesium, one has to consider how much one is getting from food. Most people do not need high doses of magnesium supplements, for that reason. The general rule of thumb is to take at least 1/2 of the suggested RDA in a supplement form. Also people with renal (kidney) disorders must have their blood checked and some physician supervision while taking magnesium supplements.

Overdosing on oral magnesium usually leads to diarrhea in normal people without kidney issues. So toxicity is difficult to reach. But in babies given enemas (Fleet's) magnesium poisoning is a real danger. Adults with eating disorders who purge this way using enemas like this can become a statistic in a poisoning event. Poisoning with magnesium yearly is rather low risk,
usually in the double digits, nationally. Elderly patients with impaired renal function are also at risk when given enemas, citrate of magnesia for X-rays, or Magnesium sulfate IV. They are not commonly poisoned orally with supplements.

The next thread I post here will be about elemental values.
Many supplements have confusing labels, and you may think you are taking something and really receiving something else.