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A placebo is an inactive substance or treatment that looks the same as, and is given the same way as, an active therapy being tested. The effects of the therapy are compared to the effects of the placebo.

Sham is a similar concept in clinical trials studying medical devices.

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NCImetathesaurus Glossary of Common Site Terms
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NIH Clinical Research Trials and You The Basics: What do the terms placebo, randomization, and blinded mean in clinical trials?

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