An adverse drug event (ADE) is any harm associated with the use of a medication, while an adverse drug reaction (ADR) specifically refers to harmful effects directly caused by a drug when taken at normal doses.

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Definitions

Adverse Drug Event (ADE):
An ADE is any injury or harm related to medication use. This can include:

• Harm from the drug itself, such as adverse reactions or overdoses

• Harm from medication errors, incorrect dosing, or failure to follow prescribed therapy​

ADEs can occur even when medications are used correctly and may result from factors such as drug interactions, provider errors, or patient misuse.

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Adverse Drug Reaction (ADR):
An ADR is a specific type of ADE that occurs when a drug causes an unintended, harmful response at normal doses used for treatment, diagnosis, or prevention. ADRs are directly linked to the drug’s pharmacological properties and are classified as:

• Type A (Augmented): Predictable, dose-dependent reactions (e.g., drowsiness from antihistamines)

• Type B (Bizarre): Unpredictable reactions unrelated to the drug’s usual effects (e.g., anaphylaxis from penicillin)

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