The number-needed-to-treat (NNT) is a measure used to describe the effectiveness of an intervention, such as treatment with a medicine.
The NNT is the number of participants who will need to be treated in order for one person to recover, or show symptom reduction, or whatever outcome is being measured in the trial. A 'perfect' result would be that every patient has a good outcome, and this would give an NNT of 1 . A large NNT means that the treatment is only effective in a small number of people: An NNT of 100 means that of 100 people treated, only 1 will have a favourable outcome.
One advantage of NNTs is that they can be easily compared for different medicines or interventions.