placebo

noun

pla·​ce·​bo plə-ˈsē-(ˌ)bō 

plural placebos

1

a

: a usually pharmacologically inert preparation prescribed more for the mental relief of the patient than for its actual effect on a disorder

b

: an inert or innocuous substance used especially in controlled experiments testing the efficacy of another substance (such as a drug)

2

: something tending to soothe

Did you know?

Doctors doing research on new treatments for disease often give one group a placebo while a second group takes the new medication. Since those in the placebo group usually believe they're getting the real thing, their own hopeful attitude may bring about improvement in their condition. Thus, for the real drug to be considered effective, it must produce even better results than the placebo. Placebos have another use as well. A doctor who suspects that a patient's physical symptoms are psychologically produced may prescribe a placebo in the hope that mentally produced symptoms can also be mentally cured.

Examples of placebo in a Sentence

Recent Examples on the Web

In any clinical trial, when the drug being studied against a placebo is found to be safe and effective, the trial is stopped. —Chicago Tribune, 2 June 2025

Under Kennedy and Food and Drug Administration Commissioner Marty Makary, the HHS has moved forward with plans to enforce a new requirement for placebo testing on all new vaccines, though how this rule will be implemented remains unclear. —Joseph Choi, The Hill, 22 May 2025

But for people at lower risk, the FDA leadership is instead pushing for additional studies to test whether people in the general population who get an annual shot have fewer COVID-19 symptoms, less-severe cases, and fewer hospitalizations and deaths compared to those receiving a placebo. —Alice Park, Time, 20 May 2025

Rotavirus, measles and HPV vaccines have been [evaluated against a placebo], and some vaccines are tested against previous versions. —NBC news, 20 May 2025

Word History

Etymology

Latin, I shall please

First Known Use

1785, in the meaning defined at sense 1a

Phrases Containing placebo

• placebo effect

Kids Definition

placebo

noun

pla·​ce·​bo plə-ˈsē-bō 

plural placebos

1

: a medicine that usually has no effect on a disease and is prescribed by a doctor for the mental relief it offers a patient

2

something that is meant to soothe

Etymology

from Latin placebo "I shall please"

Medical Definition

placebo

noun

pla·​ce·​bo plə-ˈsē-(ˌ)bō 

plural placebos

1

: a usually pharmacologically inert preparation prescribed more for the mental relief of the patient than for its actual effect on a disorder

2

: an inert or innocuous substance used especially in controlled experiments testing the efficacy of another substance (as a drug)