When considering placebo response and drop-out within PK/PD analysis, it is considered a best practice to model exactly what has occurred and what is happening within PK/PD relationships. The ideal PK/PD model will have a placebo response built into it. If a participant drops from the study, then it is advisable to model exactly what has happened. Regarding the modeling of the placebo response, it is essential to have a good understanding of the mechanism of this response. An example of this involves working with a nasal delivery drug. If you administer a nasal placebo containing a saline solution, the saline will wash out the allergens in the nasal passage, thus causing a true physical response in addition to the placebo response. Understanding this mechanistic basis is essential in creating a PK/PD model that takes the placebo response into account.