Drug allergens are substances in medications that can trigger an allergic reaction in some individuals. These reactions occur when the immune system mistakenly identifies a drug as harmful, leading to symptoms such as rashes, itching, or swelling. Common drug allergens include penicillin, sulfa drugs, and certain nonsteroidal anti-inflammatory drugs (NSAIDs). When a person is allergic to a specific drug, even a small dose can cause a reaction. It is important for patients to inform their healthcare providers about any known drug allergies to avoid potentially serious complications. In severe cases, an allergic reaction can lead to anaphylaxis, a life-threatening condition requiring immediate medical attention.