it is a powdered magnesium citrate that you can make a warm drink with water.(I used it in place of Epsom Salts w/ liver flushes...much tastier) I find it very bio available and works rapidly, it helps me sleep. It is also great for muscle spasms , aches an pains, menstrual cramps, low back pain and constipation. I have also heard the magnesium oil is the bomb too