Final answer:
Steroids are the medication added to contrast to prevent an allergic reaction due to their anti-inflammatory properties. They help control hypersensitivity reactions which may occur with contrast media.
Step-by-step explanation:
The medication that may be added to the contrast to prevent a reaction is steroids. Steroids, such as cortisol, are known for their anti-inflammatory properties and can be used to control hypersensitivity reactions, like those that may occur following contrast media administration in medical imaging. In the prevention of type III hypersensitivity reactions, anti-inflammatory steroid treatments are commonly utilized. For anaphylactic reactions, which are severe allergic reactions, epinephrine is the primary treatment.
However to mitigate milder allergic reactions and to prevent anaphylactic reactions to contrast media, premedication with steroids can be administered. This is based on their ability to down-regulate the inflammatory response in autoimmune diseases and severe arthritis, which is a similar mechanism involved in contrast media reactions.