kôrˌtəkōstârˈoid, any one of several synthetic or naturally occurring substances with the general chemical structure of steroids. They are used therapeutically to mimic or augment the effects of the naturally occurring corticosteroids, which are produced in the cortex of the adrenal gland. Corticosteroids are very powerful drugs that affect the entire body; even corticosteroids used on large areas of skin for long periods are absorbed in sufficient quantity to cause systemic effects.

Corticosteroids, as well as adrenocorticotropic hormone (ACTH), the pituitary gland substance that stimulates the adrenal cortex, have modifying effects on many diseases. Some corticosteroid derivatives mimic the action of the naturally occurring steroid hormone aldosterone, causing increased sodium retention and potassium excretion. Others have the same effects as the naturally occurring steroids cortisone and cortisol, which are classed as glucocorticoids; these affect carbohydrate and fat metabolism, reduce tissue inflammation, and suppress the body's immune defense mechanisms. Cortisone and hydrocortisone are used to treat Addison's disease, a disorder caused by underproduction of the adrenal cortex hormones. These and synthetic steroids are used extensively to treat arthritis and other rheumatoid diseases, including rheumatic heart disease. They are also used in some cases of autoimmune diseases such as systemic lupus erythematosus, in severe allergic conditions such as asthma, in allergic and inflammatory eye disorders, and in some respiratory diseases. The anti-inflammatory, itch-suppressing, and vasoconstrictive properties of steroids make them useful when applied to the skin to relieve diseases such as eczema and psoriasis and insect bites.

Because corticosteroids lower the resistance to infection, patients on steroid therapy cannot be vaccinated for smallpox or immunized. The administration of corticosteroids also causes underproduction of the natural hormones by the adrenal cortex, and so ACTH or corticosteroid therapy must always be withdrawn gradually. In addition, when used in large doses for long periods of time, the drugs can cause atrophy of the adrenal cortex. Side effects of steroid therapy include glaucoma, excess hair growth, and imbalance of many substances, including calcium, nitrogen, potassium, and sodium. Many of the synthetic corticosteroids, such as prednisone, prednisolone, triamcinolone, and betamethasone, are more potent than the naturally occurring compounds.

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