Hyphenation

Hyphenation looks small, but it changes meaning, prevents ambiguity, and reduces rework in protocols, labels, and manuscripts. This guide gives clear rules with realistic clinical, lab, and regulatory examples.

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The one-line rule

Hyphenate a compound modifier before a noun; open it after the noun.

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• Before noun: Double-blind trial, high-dose regimen, first-in-human study.

• After noun: The trial was double blind; the regimen was high dose; the study was first-in-human.

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When to hyphenate compound modifiers

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• Adjective + noun + noun: Hyphenate when the first two words act as one idea. Placebo-controlled trial; small-molecule inhibitor; next-generation sequencer.

• Noun + participle: Hyphenate. Evidence-based guideline; dose-limiting toxicity; physician-reported outcome.

• Multi-word set phrases: Keep hyphens. State-of-the-art device; proof-of-concept study; point-of-care test.

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Avoid ambiguity:

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• Correct: Small-molecule inhibitors (inhibitors of small molecules).

• Wrong: Small molecule-inhibitors (reads as “molecule-inhibitors”).

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Numbers, units, and ranges

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• Number + unit + noun (before noun): Hyphenate as a single idea.5-mg tablet; 200-µL aliquot; 12-lead ECG; 10-year follow-up.

• After the noun: Open. The tablet is 5 mg; the aliquot was 200 µL; follow-up lasted 10 years.

• Spans and ranges: Use an en dash (–) between numbers; keep unit styling consistent.10–12-week window; 5–10-mg titration range; 2–3-fold increase.

• Suspensive hyphenation (shared second element):A 5- to 10-mg increase; 6- and 12-month time points.

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Prefixes that need care

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• Most prefixes (non, pre, post, re, anti, multi, co) are closed: Noninferiority, preoperative, postoperative, read minister, antimicrobial, multivariate, costimulation.

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• Hyphenate when:

  • The prefix meets a proper noun: Anti-TNF therapy; non-EU submissions.

  • Double vowels/consonants cause misreading: Re-evaluate; co-occurrence.

  • You want to avoid ambiguity: Re-cover (cover again) vs recover (get better); re-creation vs recreation.

  • The style guide mandates it (house rules or drug/brand constraints).

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Some examples to remember

Fixed scientific compounds (commonly hyphenated)

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• First-in-human, open-label, dose-escalation, single-arm, double-blind, intent-to-treat, per-protocol (population), real-world (evidence/cohort), next-generation (sequencing).

• Note usage after the noun: The cohort was real world; the device is state-of-the-art.

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AMA/medical style notes you’ll use daily

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• Disease eponyms: Non-possessive (Parkinson's disease, Alzheimer disease). Hyphenation rules still apply to modifiers around them: Early-onset Alzheimer's disease; treatment-resistant Parkinson's disease.

• Trial descriptors: Randomized controlled trial (no hyphen between randomized and controlled), but compound forms before a noun take hyphens: Randomized, placebo-controlled, double-blind phase 3 trial.

• “Real-world evidence” before a noun is hyphenated; after the noun it is open: The evidence was real-world.

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Labeling, CMC, and quality documents

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• Keep dosing and storage lines precise: Administer a 300-mg dose; perform a 12-hour fast.

• Method attributes before nouns are hyphenated: High-performance liquid chromatography (HPLC); mass-spectrometry-based assay.

• Validation phrases: ICH-compliant method; risk-based approach; life-cycle-managed change control.

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Common pitfalls and quick fixes

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• Dangling modifier

  • Wrong: Patients received high dose chemotherapy

  • Right (before noun): Patients received high-dose chemotherapy

  • Right (after noun): The chemotherapy dose was high

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• Unit clusters without clarity

  • Wrong: 5 mg 10 mg titration

  • Right: 5- 10-mg titration

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• Hyphen vs en dash

  • Hyphen joins words (double-blind).

  • En dash marks range (10–12 weeks) or complex links (dose–response curve per some house styles).

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• Over-hyphenation after a noun

  • Wrong: The study was first-in-human

  • Right: The study was first in humans

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• Open compounds that need a hyphen

  • Wrong: Point-of-care testing device

  • Right: Point-of-care testing device

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Quick decision tips

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1. Before a noun and acting as one idea? Hyphenate.

2. After the noun? Usually open.

3. Numbers + units before noun? Hyphenate (5-mg tablet).

4. Ranges/spans? Use en dash (10–12 weeks); use suspensive hyphens (5 to 10 mg).

5. Prefixes? Close by default; hyphenate for clarity, proper nouns, or mandated style.

6. Unsure? Read aloud. If the reader may misgroup the words, add the hyphen.