The ‘number need to treat’: does it help clinical decision making?


The number needed to treat (NNT) is an increasingly popular way of presenting the effects of treatment. However, the NNT varies markedly depending on the baseline risk of patients, the outcome considered, and the clinical setting. Furthermore geographic and secular trends make the NNT unstable between places and over time. Particular caution is needed in deriving the NNT from pooled absolute risk differences in meta-analysis. In general, the NNT should be calculated by applying the relative risk reduction on treatment estimated by trials or meta-analysis to populations of specified absolute high, average or low risk to illustrate a range of possible NNTs.

Author information

Correspondence to S Ebrahim.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Ebrahim, S., Smith, G. The ‘number need to treat’: does it help clinical decision making?. J Hum Hypertens 13, 721–724 (1999).

Download citation


  • meta-analysis
  • hypertension
  • randomised controlled trials

Further reading