What are common signs of an allergic reaction to medication?

The signs of an allergic reaction to medication are primarily related to the body's immune response to a substance it mistakenly identifies as harmful. Common symptoms include rash, itching, swelling, and difficulty breathing.

A rash may appear as hives or welts on the skin, indicating that the immune system is reacting against the medication. Itching is often associated with this skin response. Swelling, particularly in areas such as the face, lips, or throat, can occur due to an allergic reaction, leading to potential airway obstruction, which makes difficulty breathing a critical and life-threatening symptom. This combination of symptoms is characteristic of reactions such as anaphylaxis, a severe allergic reaction that requires immediate medical attention.

Other options listed, like headache and nausea; dry mouth and fatigue; or drowsiness and dizziness, may be side effects of medications but do not specifically indicate an allergy. These symptoms can arise from various causes unrelated to an immune response, making option A the correct choice in identifying common signs of an allergic reaction.