Number needed to treat (NNT)

The number needed to treat (NNT) is the average number of patients you must treat for one extra patient to benefit, versus a control. Laupacis, Sackett, and Roberts introduced it in the New England Journal of Medicine (1988). NNT is the reciprocal of the absolute risk reduction (ARR): NNT = 1 ÷ ARR. And ARR is just the control-arm event rate minus the treatment-arm event rate. Because NNT ties benefit to a concrete head-count, it makes the absolute effect size clear. An NNT of 50 means 50 people must be treated for one to avoid the target outcome. In aging and longevity medicine, where the goal is preventing heart disease, cancer, or functional decline, NNT values are often far higher than intuition suggests. A re-analysis of the JUPITER trial (Ridker et al., 2009) found an NNT of about 95 over 2 years, for the primary composite endpoint with rosuvastatin. (The 5-year NNT was roughly 20.) In true primary prevention for healthy adults, statins carry NNTs of 60 to 270, depending on the endpoint and risk group. NNT depends heavily on baseline risk, the observation period, and the comparator. So a figure cited without that context can mislead you. And confidence intervals from the ARR are essential to read it properly.

Last reviewed: June 22, 2026

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