Number Needed to Treat (NNT) / Number Needed to Harm (NNH)
Calculates NNT or NNH from event rates in treatment and control groups. Fundamental EBM tool for communicating treatment effectiveness.
Score interpretation
NNT 1-5: Highly effective. Treat 1-5 patients to prevent 1 outcome.
→ Strong clinical benefit. High priority for eligible patients.
NNT 5-20: Moderate benefit. Consider absolute risk and side effects.
→ Weigh benefit vs risk. Discuss with patient.
NNT >20: Limited benefit in this population.
→ Critically appraise evidence. Consider alternative strategies.
Interpretation bands for the NNT/NNH. Apply clinical judgement and local guidance.
References
- Laupacis A, et al. An assessment of clinically useful measures of the consequences of treatment. N Engl J Med. 1988;318(26):1728-1733.
Related
Curated clinical cross-links plus same-class fallbacks.
- Emollient bath and shower products, paraffin-containing · Paraffin-based bath/shower emollient
- Emollient creams and ointments, hydrogenated castor oil-containing · Hydrogenated castor oil-based emollient
- Dimeticone · Topical pediculicide (silicone-based)
- Prednisolone (Oral — General Medicine) · Oral Corticosteroid
- Influenza vaccine (inactivated) · Vaccine
- Artemether with Lumefantrine · Artemisinin-Based Combination Antimalarial (ACT)
Featured in these MRCEM clinical pathways
The NNT/NNH is covered in detail — with RCEM/NICE evidence base, indications and pitfalls — in the following exam-focused pathways on our sister siteReviseMRCEM.
MRCEM Primary / Intermediate / OSCE candidates: each pathway includes exam-style questions, RCEM/NICE citations, and FAQ summaries.
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.