Dexamethasone is a synthetic glucorticoid (or corticosteroid) drug which is used chiefly as a high-powered anti-inflammatory. It is known by several trade names, including Decadron, Hexadrol and Dexone.
It is used to combat the inflammation associated with autoimmune diseases like birdshot retinochoroidopathy, lupus and multiple sclerosis, to aid in destroying certain forms of cancer and as an antiemetic to control nausea and vomiting. In this latter role it is sometimes used alone, but more frequently with ondansetron, granisetron or dolasetron, with which it has a strongly synergistic effect. (In studies, dexamethasone and ondansetron together have been shown to be more than four times more effective than ondansetron alone). It is not compatible with doxorubicin, and can cause serious side effects.
Long-term administration of dexamethasone can lead to chronically depressed cortisol levels, osteopenia and a host of other potential medical problems, so typically the drug is not administered for any longer than is absolutely necessary. Abruptly ceasing treatment with the drug can cause serious withdrawal effects, though it is not addictive in the traditional sense. | 
