Steroids describe a wide class of drugs that are generally prescribed for their anti-inflammatory effect. They're commonly used to treat autoimmune diseases, chronic breathing problems, and severe muscle injuries. Some steroids, such as testosterone, are naturally produced by the body in small quantities.
However, because steroids suppress the immune system, their side effects must be closely monitored. Patients can easily become dependent on the drug and may not be able to stop using it without suffering a rebound of the very symptoms the drug was designed to treat. For example, a person prescribed aerosol steroids (a "puffer") for lung problems may suffer respiratory arrest if the drug is cut off entirely. In most cases, the patient has to be given progressively lower doses of the drug, essentially weaning them off.
Topical corticosteroid creams can cause addiction when used long term and can cause a type of eczema known as Red Skin Syndrome.
Steroids are often abused by athletes as they encourage muscle growth and lessen muscle pain and inflammation from training. However, the side effects can be severe, including weight gain, edema, and personality changes.