Understanding Number Needed to Treat (NNT) of 6

What NNT Measures

NNT is calculated as the inverse of the absolute risk reduction (ARR): NNT = 1/ARR × 100, as stated by the American College of Emergency Physicians 1, 2, 3
When ARR = 16.67%, the NNT equals 6 (1/0.1667 = 6), according to the British Journal of Psychiatry 4

For every 6 patients treated with the intervention, 5 patients would have the same outcome whether they received the intervention or control, as reported by the American College of Emergency Physicians 1, 3

An NNT of 6 is substantially better than examples such as Evolocumab (Repatha) with an NNT of 67 over 2.2 years, and Ezetimibe plus simvastatin with an NNT of 50 over 6 years, indicating a more effective intervention, as compared by the British Journal of Psychiatry and other sources 4, 5

NNT should be considered alongside the time period over which the NNT applies, as noted by the British Journal of Psychiatry 4

NNT values are specific to the population being studied, the specific intervention being used, and the time period of observation, as stated by the American College of Emergency Physicians and the British Journal of Psychiatry 1, 4
Always check if the NNT is statistically significant, as recommended by the Annals of the Rheumatic Diseases 6

Failing to consider the time period over which the NNT applies can lead to misinterpretation, as warned by the British Journal of Psychiatry 4

An NNT of 16, as seen with tamoxifen for breast cancer prevention, is considered clinically meaningful, preventing one additional breast cancer per 16 women treated, according to the American Society of Clinical Oncology 7
NNT values between 10-20 generally indicate strong clinical benefit, as demonstrated in cardiovascular prevention where NNT of 22 for composite CV events and 43 for heart failure were considered acceptable benchmarks by the American Heart Association 8
NNT values of 20-50 represent acceptable therapeutic benefit depending on the severity of the condition being prevented, as stated by the American College of Cardiology 8, 7
For serious outcomes like stroke or myocardial infarction, NNT values up to 50 may justify treatment, according to the American Heart Association 8
When NNT exceeds 100, the intervention requires treating large numbers of patients for minimal population-level benefit, as noted by the American College of Cardiology 8

When NNH approaches or falls below NNT, the intervention may cause more harm than benefit, as seen in the case of tamoxifen, which has an NNT of 16 for breast cancer prevention versus NNH of 115 for venous thromboembolism and NNH of 73 for endometrial cancer, according to the American Society of Clinical Oncology 7
The therapeutic index (NNH/NNT ratio) should exceed 2-3 for favorable risk-benefit profiles, as recommended by the American Society of Clinical Oncology 7