What is a key symptom of an allergic reaction to medication?

A key symptom of an allergic reaction to medication is the presence of a rash. Allergic reactions often manifest through skin changes, including hives or a generalized rash, which may occur shortly after exposure to the offending medication. This rash may vary in appearance and can be associated with itching, redness, and swelling, indicating the body's immune response to what it mistakenly identifies as a harmful substance. Recognizing dermatological symptoms like rash is crucial in identifying allergic reactions early and avoiding potentially severe outcomes.

While other symptoms such as diarrhea, severe headache, and fatigue can occur for various reasons, they are not specific indicators of an allergic reaction to medication. Diarrhea may be related to gastrointestinal issues, headaches may arise from tension or other causes, and fatigue can result from many health conditions, making them less reliable in identifying drug allergies. Consequently, when assessing an allergic reaction, a rash stands out as a definitive sign that warrants immediate attention and evaluation.