Phosphatidylserine, or PS for short, is a member of a class of chemical compounds known as phospholipids. PS is an essential component in all our cells; specifically, it is a major component of the cell membrane. The cell membrane is a kind of "skin" that surrounds living cells. Besides keeping cells intact, this membrane performs vital functions such as moving nutrients into cells and pumping waste products out of them. PS plays an important role in many of these functions.

Good evidence suggests that PS can help declining mental function and depression in the elderly, and it is widely used for this purpose in Italy, Scandinavia, and other parts of Europe. PS has also been marketed as a "brain booster" for people of all ages, said to sharpen memory and increase thinking ability. However, the evidence to support this use is incomplete and inconsistent.