Lithium is usually found in nature not as a metal but as lithium salts. Its name comes from lithos, the Greek word for "stone," as the lithium crystals are beautiful and very hard rocks.

The mineral petalite (which contains lithium) was discovered by the Brazilian scientist José Bonifácio de Andrada e Silva towards the end of the 18th century while visiting Sweden. Lithium was discovered by Johan August Arfvedson in 1817 during an analysis of petalite ore, an ore now recognised to be LiAl(Si₂O₅)₂, taken from the Swedish island of Utö. Arfvedson subsequently discovered lithium in the minerals spodumene and lepidolite. C.G. Gmelin observed in 1818 that lithium salts colour flames bright red. Neither Gmelin nor Arfvedson were able to isolate the element itself from lithium salts. The first isolation of elemental lithium was achieved later by W.T. Brande and Sir Humphrey Davy by the electrolysis of lithium oxide. In 1855, Bunsen and Mattiessen isolated larger quantities of the metal by electrolysis of lithium chloride. In 1923 the first commercial production of lithium metal was achieved by Metallgesellschaft AG in Germany using the electrolysis of a molten mixture of lithium chloride and potassium chloride, exploiting a suggestion made by Guntz in 1893.

Aside from hydrogen, which is present in almost all of life, lithium is the lightest element in use. It is unique among the minerals in that it is used in medical treatment of manic-depressive disorders, commonly as lithium carbonate. It is chemically similar to sodium and can displace sodium (and vice versa) in many bodily reactions. Its involvement in sodium transport across cell membranes probably accounts for lithium's therapeutic support of people with manic disorders. Although it has been used in this area since about 1950, its acceptance has been slow, possibly because it is a natural mineral and not as profitable for the pharmaceutical companies as synthetic drugs. Recent evidence indicates that lithium may be an essential element, needed in trace amounts (minute in comparison to the high doses used in treatment).

We have in our body only about 2-3 mg. of lithium. Absorption from the intestine is good, about 70-90 percent. People with mania often have very good absorption of lithium. Excess lithium is eliminated in urine and feces.

Lithium compounds are regarded as slightly toxic, and perhaps more so than the other Group 1 elements. Lithium appears not to have a biological role, which is not to say that lithium compounds do not have an affect. Sometimes, lithium-based drugs such as lithium carbonate (Li₂CO₃) are used to treat manic-depressive disorders in doses of around 0.5 g - 2 g daily. Some side effects are known. Ingestion of large amounts of lithium results in drowsiness, slurred speech, vomiting, and other symptoms. Excess lithium poisons the central nervous system.

Lithium's main use is in treating manic-depressive disorders, for which it is used in what could be considered megadosages. Certain depression problems, probably those sensitive to sodium transport difficulties, may be helped by lithium, even where there is little or no manic component. Manic symptoms of insomnia, hyperactivity, talkativeness, grandiose thinking, and delusions can usually be controlled with lithium therapy. Dosages of between 600 and 1000 mg. per day are needed to obtain the appropriate blood level to treat mania.

Lithium has occasionally been used in treating alcoholism, where it apparently decreased the taste for alcohol and generated a more cheerful attitude toward life. Lithium treatment does, however, produce some side effects, such as a metallic taste in the mouth, increased thirst, and more frequent urination. It is not routinely taken as a nutritional supplement but is used primarily as a medicinal drug.