Which of the following is considered an adverse reaction?

Anaphylaxis is categorized as a severe, potentially life-threatening allergic reaction that occurs rapidly after exposure to an allergen. This reaction can involve multiple systems of the body, leading to symptoms such as difficulty breathing, swelling of the throat, a drastic drop in blood pressure, and potential loss of consciousness. Because of its gravity and the immediate medical attention it requires, anaphylaxis is classified as an adverse reaction.

In contrast, while nausea, headache, and fatigue can be unpleasant and are commonly experienced after the use of medications or due to various health conditions, they are typically classified as side effects rather than adverse reactions. Side effects can vary in severity and may not require urgent medical intervention, unlike the serious nature of anaphylaxis, which can escalate quickly and poses significant risk to an individual's health. Understanding the distinction between adverse reactions and common side effects is crucial in healthcare, as it guides how professionals respond to patient care and treatment plans.