Lithium is a medicine of the first choice in the preventive treatment of bipolar affective disorder. It is also used to enhance the treatment of drug resistant depression. How excatly this element acts is not yet fully understood. Lithium influences the transportation of sodium via cellular membranes (sodium-potassium ATPase dependant), has an inhibitory influence on the second transmitter system (connected with phosphatidylinositol), thus probably acting as a stabiliser of inter cellular processes. Lithium does not associate with plasmatic proteins and is almost entirely excreted by kidneys. The side effects of the medicine are linked to its influence on the central nervous system and on the renal transportation of electrolytes as well as the narrow therapeutic index of the medicine, which can cause intoxication if the recommended doses are not when medical recommendations are not observed. The undesirable effects are more intensive when the level of lithium in the blood plasma increases. Among the most common side effects are stomachaches, nausea, diarrhoea, lack of appetite, polydipsia, polyuria, shaking hands, headaches, sleepiness or deterioration of memory. Complications during lithium therapy listed in literature are ataxia, dysarthria, nystagmus and extrapyramidal symptoms, but the most severe complication is lithium poisoning. Lithium can be applied for a long-term maintenance treatment, which limits recurrence of the disease and improves the patient’s family, social and occupational life. The inferior quality of life among patients with affective disease can result from the disorder itself or can develop on the somatic grounds, appear due to abuse of tobacco or alcohol, or else be a side effect of other medicines taken by the patient. Good co-operation with the patient during the therapy can lessen the pronouncement of undesirable symptoms and complications of a lithium treatment, and this in turn can improve of the quality of the patient’s life.