An RCT may be blinded, (also called "masked") by "procedures that prevent study participants, caregivers, or outcome assessors from knowing which intervention was received." Unlike allocation concealment, blinding is sometimes inappropriate or impossible to perform in an RCT; for example, if an RCT involves a treatment in which active participation of the patient is necessary (e.g., physical therapy), participants cannot be blinded to the intervention.

Traditionally, blinded RCTs have been classified as "single-blind," "double-blind," or "triple-blind"; however, in 2001 and 2006 two studies showed that these terms have different meanings for different people. The 2010 CONSORT Statement specifies that authors and editors should not use the terms "single-blind," "double-blind," and "triple-blind"; instead, reports of blinded RCT should discuss "If done, who was blinded after assignment to interventions (for example, participants, care providers, those assessing outcomes) and how."

RCTs without blinding are referred to as "unblinded", "open", or (if the intervention is a medication) "open-label". In 2008 a study concluded that the results of unblinded RCTs tended to be biased toward beneficial effects only if the RCTs' outcomes were subjective as opposed to objective;[47] for example, in an RCT of treatments for multiple sclerosis, unblinded neurologists (but not the blinded neurologists) felt that the treatments were beneficial. In pragmatic RCTs, although the participants and providers are often unblinded, it is "still desirable and often possible to blind the assessor or obtain an objective source of data for evaluation of outcomes."

https://en.wikipedia.org/wiki/Randomized_controlled_trial#Bl...

Prueba de ciego único
En una prueba con ciego único, el investigador conoce los detalles del tratamiento pero el paciente no. Como el paciente no sabe que tratamiento está recibiendo (el tratamiento nuevo u otro) no debería haber efecto placebo. En la práctica, como el investigador sabe, es posible que trate en forma diferente a los pacientes o en forma subconsciente oculte a los pacientes detalles importantes relacionados al tratamiento, influyendo de esta forma los resultados del estudio.

https://es.wikipedia.org/wiki/Prueba_controlada_aleatorizada...