Which statement best distinguishes a side effect from an adverse drug reaction?

• A. A side effect is always harmful; an adverse drug reaction is never harmful.
• B. A side effect is an expected secondary effect; an adverse drug reaction is an unintended harm caused by the drug.
• C. A side effect is only temporary; an adverse drug reaction is permanent.
• D. A side effect occurs only with IV meds; adverse drug reaction occurs with any route.

Answer: (B)

Understand that a side effect is a known, expected secondary effect of a drug that’s not the intended therapeutic benefit. It can be mild or even harmless and is something you anticipate when using the medication. An adverse drug reaction, on the other hand, is an unintended harm caused by the drug at normal doses and is not part of the intended effect. So the best statement captures this distinction by saying a side effect is an expected secondary effect, while an adverse drug reaction is an unintended harm.

For example, drowsiness from an antihistamine is a side effect you expect, whereas liver injury from a medication would be considered an adverse drug reaction. The other options misstate the relationship by implying side effects are always harmful, by claiming side effects are temporary-only, or by tying side effects to a single route of administration.