Where do wrong words hide in the Adverse Reactions section?

In our view, in the reaction names and the words that rank them, and most of all in the long tables and lists where readers skim. 21 CFR 201.57 says the section must describe the overall adverse reaction profile of the drug and list the reactions, ordered by body system, severity or decreasing frequency, so a correctly spelled wrong word can rename a reaction or move it to the wrong group. Spellcheck passes it.

This page is general information, not legal or regulatory advice.

For the other sections, see how to proofread a drug label for meaning, section by section. This page covers the prescription Adverse Reactions section. For the word adverse itself, where it belongs and how to search for a swap of it, see where adverse belongs on a drug label.

What the section contains

21 CFR 201.57 defines an adverse reaction, for prescription labeling, as an undesirable effect reasonably associated with use of a drug. It says the definition covers only those adverse events where there is some basis to believe the drug caused them. The rule then says the section must:

• List the adverse reactions that occur with the drug, preceded by the information needed to interpret them, such as the extent of exposure in clinical trials.
• Group them by body system, by severity or in decreasing order of frequency, and within a group list them by decreasing frequency, or by decreasing severity when frequency can't be reliably determined.
• For clinical trials, give the rate for the drug and for comparators such as placebo, unless that can't be determined or would mislead.

The FDA's guidance on this section says the start of the section should identify the most clinically significant reactions and cross-reference those described in more detail elsewhere, especially in the Boxed Warning or Warnings and Precautions. It says common reactions are typically presented in tables to permit side-by-side comparison, and that exhaustive lists of reported events, including infrequent and minor ones, should be avoided because they obscure the more meaningful information.

Tables and lists: where wrong words hide

Our view: reaction tables invite the eye down the numbers, not across the words. The reaction name in each row is read once, if at all, and the column headings that say which group is which are read at the top and then forgotten. A swap in a row name or a heading still leaves the tables looking tidy.

Made-up example: a row in the clinical trials tables reads "hypotension" where the study term was "hypertension". Both are real reactions, the rates beside them are correct, and the row now reports a different effect.

Reaction names that look alike

Many reaction names differ by a prefix or a few letters. For a list of those, see confusable clinical terms.

Matching the rest of the label

• Warnings and Precautions and the Boxed Warning. The guidance asks for cross-references to reactions described there. Check that each cross-referenced reaction carries the same name in both places. See wrong words in Warnings and Precautions and wrong words in a Boxed Warning.
• Highlights. 21 CFR 201.57 says Highlights must list the most frequently occurring adverse reactions. Check that the Highlights list names the same reactions as the full section.
• Patient labeling. Check that the plain words used for each reaction mean the same thing as the clinical term. See Medication Guide and patient labeling errors.

How to read the section for meaning

Practice advice:

• Read the tables across, not down: say the reaction name, then the group, then the rate.
• Read the column headings again halfway down long tables.
• Check the order the rule asks for. A reaction that seems out of order can be a sign the name is wrong.
• Search for each reaction name in Highlights and Warnings and Precautions, and confirm it's spelled and named the same way.

This is our reading of public guidance, not legal or regulatory advice.

Sources

• eCFR: 21 CFR 201.57
• FDA guidance: Adverse Reactions Section of Labeling for Human Prescription Drug and Biological Products — Content and Format
• eCFR: 21 CFR 201.66

Last reviewed: October 18, 2026

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What's in the Adverse Reactions section?

21 CFR 201.57 says it must describe the overall adverse reaction profile of the drug and list the reactions, grouped by body system, severity or decreasing frequency.

Where do wrong words hide in Adverse Reactions?

In our view: in reaction names that look alike, and in the row names and column headings of long tables.

Does Drug Facts have an Adverse Reactions section?

No. It's a prescription labeling section. Drug Facts uses the fixed headings set by 21 CFR 201.66, and Adverse Reactions isn't one of them.

How do I proofread an Adverse Reactions section for meaning?

Practice advice: read the tables across, recheck the column headings, and match each reaction name against Highlights and Warnings and Precautions.