Dexamethasone is a corticosteroid that’s used to treat many inflammatory conditions, including allergic reactions and certain autoimmune conditions. If you’ve been taking dexamethasone for a long time, you’re at higher risk for side effects like weight gain and weakened bones. Dexamethasone also has many drug interactions, so make sure to tell your provider and pharmacist what medications you’re taking before starting this steroid. This medication is available as oral tablets and solutions, as well as an injection that’s usually given in a healthcare setting.