Magnesium glycinate is considered the best type of magnesium for sleep. It is easily absorbed by the body and has a calming effect on the nervous system and muscles. Magnesium citrate is also a common form of magnesium used in supplements, but magnesium glycinate is generally considered to be more effective for bettering sleep. Magnesium oxide and chloride have a much milder laxative effect than other kinds, but they are not recommended for sleep. When looking for the best magnesium supplement for sleep, it is important to pay attention to the type of magnesium used in the supplement. Magnesium supplements are not advised by the U.S. National Library of Medicine, and it is better to consume the nutrient through the diet. However, if you still plan to take a magnesium supplement, magnesium glycinate or magnesium citrate at 200 milligrams is recommended.