Lithium is a metallic element (atomic number 3) that is highly reactive with water and has several technological uses, such as high-power batteries for laptop computers. However, in medicine, salts of lithium combined with another element are used in the treatment of types of mental illness that cause mood disorders, most commonly bipolar disorder. Lithium compounds were also used in the treatment of gout in the 19th century.
Lithium has severe side effects including weight gain, diabetes insipidus, hypothyroidism and nystagmus. It can rapidly cause dehydration and levels of the chemical in the blood must be constantly monitored to prevent toxicity.
The soft drink 7up contained lithium until 1948, when the form of lithium used was made a controlled substance.