Glucocorticoids have been used in clinical medicine since 1940s. Despite the time-long use they are still a subject of active ongoing research. We describe the mode of action, pharmacology and side effects to enable proper prescription of these drugs. Glucocorticoids exert genomic and non-genomic effects, the latter become important at higher doses. The nomenclature of dosage ranges and the principles of dosage adjustments are given. Glucocortioid use is associated with frequent and important side effects in numerous organ systems. Prophylactic treatments for osteoporosis and infections are described. The suppression of hypothalamic-hypophyseal hormonal axis determines the need for gradual glucocorticoid withdrawal and supplementation after discontinuation. Finally, glucocorticoid withdrawal syndrome is described.