Lithium is a drug commonly used to treat bipolar disorder and depressive disorders. It is a positively charged element or particle that is similar to sodium and potassium. It interferes at several places inside cells and on the cell surface with other positively charged atoms such as sodium, potassium, calcium, and magnesium, which are important in many cellular functions. It interferes with the synthesis and retake of chemical messengers by which nerves communicate with each other (neurotransmitters). It also affects the concentrations of tryptophan and serotonin in the brain. In addition, it increases the production of white blood cells in the bone marrow.