If you are sensitive to the laxative actions of magnesium, then a delayed acting type is best. Like SlowMag (generic Mag 64).

If you don't easily get loose on magnesium then there are chelated types you can use.
magnesium Lactate
magnesium glycinate (not expensive)
magnesium citrate (in moderation--high dose=laxative)
magnesium malate (good for fibro people)
magnesium taurate (hard to find and more expensive)

I like the powdered form Ionic Fizz too. It works FAST.
You can alter the scoop size if it gets too laxative for you.
example for large tub:
http://www.vitacost.com/Pure-Essence...berry-Lemonade
http://www.iherb.com/ProductDetails....&pid=3197&at=0
I like the silica in it...this is good for tendons and connective tissue repair.

Just stay away from magnesium oxide--- this is very common and in many formulas. Even if the label says, "from magnesium oxide and chelate" avoid it. It will be all oxide.
I've called manufacturers and they cannot tell me how much of each is in their product...so I assume it is all oxide since that is the cheapest form. Oxide is very poorly absorbed.
You get about 8mg inside you from a 400mg tablet. So basically it is useless.

Some foods are good magnesium sources. I often do the nuts...say for lunch. 3 oz of unsalted almonds have 270mg of magnesium.

This website is really good for food values:
almonds:
http://www.nutritiondata.com/facts/n...roducts/3086/2

Beans:
http://www.nutritiondata.com/facts/l...roducts/4298/2

Broccoli:
http://www.nutritiondata.com/facts/v...roducts/2361/2

Watch serving sizes, when looking up nutrients...they vary.
Also watch nutrition labels when buying supplements.
Sometimes for magnesium it will say, 4 capsules provide:
or 2 caplets provide...then give the chart. So sometimes people miss that they have to take more than one tablet/cap to get what the chart shows. Since both Calcium and magnesium supplements tend to be large in size, the number of caps is often raised.