In this review, the authors present data on the biological effects of lithium in human and animal body and the subsequent manifestations of these effects. Since the lithium ion radius is close to that of magnesium, lithium ion can compete with magnesium as cofactor of certain magnesium-dependent enzymes. Numerous studies have shown lithium to be an inhibitor of glycogen synthase kinase 3. It also inhibits the phosphatases involved in the metabolism of phosphoinositides and phosphoadenylate 3′-nucleotidase. As these enzymes play an important and sometimes crucial role in signaling systems activity, lithium is able to affect the essential physiological, adaptive and pathogenetic processes.