Information on steroids used as part of ATG treatment This information fact sheet is for patients who have been prescribed steroids as part of Anti-Thymocyte Globulin (ATG) treatment. It explains what they are, how they work and any risks or side effects. You can download the fact sheet here. What are steroids? ‘Steroid’ is a term that describes a class of chemical compound that is naturally synthesised in the body but can also be manufactured (synthetic steroids) and performs important functions in the body, including suppressinginflammation. Why are steroids used? Steroids are important as they help to administer ATG treatment safely. They can reduce any immediate reactions or delayed ones, such as serum sickness.