A review of the use of the number needed to treat to evaluate the efficacy of analgesics.

Standardized measures of efficacy are needed to compare analgesic efficacy across trials. The number needed to treat (NNT) is considered a statistically robust and readily interpretable measure to rank the efficacy of treatments, including analgesics. The NNT has become widely utilized to compare the efficacy of chronic pain treatments, helping physicians make treatment decisions and informing decisions for market access, reimbursement, and treatment guidelines. However, the NNT is associated with specific weaknesses in calculation and interpretation not associated with other methods for integrating trial data. These weaknesses include distortions in calculation as placebo effects approach treatment effects, with the possibility of infinite values; difficulties in estimating the NNT's confidence interval; and difficulties in interpretation. The NNT also requires selecting cutoffs of the original variable for dichotomization, with the NNT often changing depending on the cutoff. The NNT also suffers from problems common to other placebo-adjusted endpoints, including being sensitive to study-related and external factors (eg, year of publication). Therefore, clinicians and other stakeholders need to be aware of these issues to correctly calculate, use, and interpret the NNT. Nevertheless, efficacy, as measured by any variable, is only one aspect of a treatment to be considered in determining its place in therapy.