How many patients must receive a drug to prevent a single tragedy?

Health · Published 18 October 2026 Swipe more like this →

In short: In medicine, success is often measured by percentages, but those numbers can mask the true scale of impact. To understand a treatment's real-world power, clinicians use the Number Needed to Treat (NNT)—a metric that reveals exactly how many people must undergo therapy to avert one specific bad outcome.

The Number Needed to Treat (NNT) is an epidemiological tool used to communicate the effectiveness of a healthcare intervention. Mathematically, it is the inverse of the absolute risk reduction, representing the average number of patients who must be treated to prevent one additional bad outcome. While a theoretical NNT of 1 would mean every single patient benefits, in practice, the value is always rounded up to the nearest whole number. A higher NNT indicates a less effective treatment, whereas a lower NNT suggests a more potent intervention.

The utility of NNT becomes most apparent when evaluating high-stakes clinical endpoints, such as death or organ failure. For example, in patients with primary biliary cholangitis (PBC) who do not achieve alkaline phosphatase (ALP) normalization on ursodeoxycholic acid, the use of bezafibrate (BZF) has shown significant potential. Researchers estimating the impact of BZF found that to prevent one instance of liver transplantation or death within five years, the NNT was 15 (95% CI 11-26). Over a ten-year horizon, this efficiency increased, with an NNT of 7 (95% CI 6-13).

The metric also allows for nuanced, personalized medicine. The efficacy of BZF appears to scale with the patient's initial ALP levels. For those with higher levels (≥3.0 × the upper limit of normal), the 10-year NNT to prevent transplantation or death dropped to just 4 (95% CI 3-8). However, NNT is not without controversy; it can be subject to bias, lacks reliable confidence intervals in some studies, and can vary significantly depending on the specific time-point of calculation. Despite these complexities, it remains a vital tool for shared decision-making between physicians and patients.

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