[N-of-1 trials: the one and only]

Personalized care is a topical issue: the demand for an optimal, individualized treatment instead of uniformity and strict guidelines in increasing. Implementing these ideals in clinical practice often appears to be challenging, as a result of heterogeneity in treatment effects and the influence of patient-specific factors. N-of-1 trials are double-blind, randomized, placebo-controlled trials in an individual patient and can be used to objectively examine the (side)effects of a specific drug, and to compare two or more drugs or variants of the same drug. The results can be used when aiming of deprescribing, but also for evaluating patient-reported intolerances or (in)effectiveness. This article discusses the use and advantages of N-of-1-trials in clinical practice, and addresses its specific concerns and possibilities. The N-of-1-trial is an effective, cost-reducing method to evaluate the effects of a certain drug, which is accessible to nearly every physician and can contribute to safe and effective personalized medicine.