Severe allergic reactions, known as anaphylaxis, are scary, and it can sometimes be hard to determine the cause. A new medically challenging case presented at this year’s American College of Allergy, Asthma and Immunology (ACAAI) Annual Scientific Meeting reports a situation in which a non-steroidal anti-inflammatory drug (NSAID) caused an anaphylactic reaction in a female runner. NSAIDs are medicines that are widely used to relieve pain, reduce inflammation, and bring down a high temperature.