Which type of trial allows a patient to receive both treatments being compared?

A crossover trial is designed specifically to allow patients to receive both treatments being compared during the course of the study. In this type of trial, participants receive one treatment for a certain period, followed by a washout period, after which they receive the other treatment. This design is particularly beneficial because it allows each participant to serve as their own control, which can reduce variability and improve the accuracy of the comparison between the two treatments.

The structure of a crossover trial enables researchers to assess the effects of both interventions on the same individual, which can lead to more robust conclusions regarding the efficacy and safety of the treatments. This design is ideal for conditions where the effects of treatments can be reversible and not cumulative over time.

In contrast, the other types of trials do not allow for patients to receive both treatments. For instance, in a parallel trial, participants are randomly assigned to different groups that either receive one treatment or another, without crossover. Similarly, double blind and single blind trials can be either parallel or crossover, but they primarily focus on masking treatments to reduce bias rather than allowing for both treatments to be administered to a single participant.