What is an adverse drug effect (adverse drug reaction)?

• A. A harmful, unintended reaction to a drug administered at normal dosage
• B. A mild symptom that improves with dosage
• C. The intended therapeutic outcome of a drug
• D. A drug interaction that enhances antibiotic activity

Answer: (A)

An adverse drug reaction is a harmful or unintended response to a medication given at normal, approved doses. It isn’t the intended therapeutic effect, and it can range from mild side effects to serious, life-threatening effects. This distinguishes it from therapeutic benefits and from drug interactions, which involve how drugs affect each other rather than how a single drug harms a patient. For example, a rash after starting penicillin is an adverse reaction, whereas the drug’s job is to treat an infection; an interaction that boosts antibiotic activity is about interactions, not an adverse response. ADRs can be dose-related or idiosyncratic, but the key point is that they are undesired and potentially harmful.