Placebo
What a definition is not
A definition is SPEQ’s plain-language decode of how a term is used in practice, cited to the documents that define it. It is a practitioner reference, not legal or regulatory advice, it does not replace the definition in the source, and where a regulator’s wording differs the regulator’s wording governs.
An inactive substance or intervention, indistinguishable in appearance and administration from the investigational product, used as a comparator to isolate the treatment’s pharmacological effect from expectation and natural disease fluctuation. Use of a placebo control raises ethical considerations that must be justified against the availability of established effective therapy.
A placebo-controlled design supports assay sensitivity — the trial’s ability to distinguish an effective treatment from an ineffective one — by separating the drug’s true pharmacological effect from placebo response and the natural course of the disease.
Its ethical use is constrained: a placebo arm is generally justified only where no established effective treatment exists for the condition, or where withholding treatment for the trial’s duration poses no risk of serious or irreversible harm. Where an effective therapy exists, add-on designs — placebo plus standard of care, compared against investigational product plus standard of care — are commonly used instead.
Subjects must give informed consent that explicitly discloses the possibility of placebo assignment and explains the rationale, so the ethical justification is transparent to the person bearing the risk.
- —Justified primarily where no established effective treatment exists, or where withholding it poses no risk of serious harm.
- —Add-on (placebo plus standard of care) designs are often used when withholding standard therapy is not ethical.
- —Supports assay sensitivity — the trial’s ability to distinguish an effective treatment from an ineffective one.
- —Requires informed consent that explicitly discloses the possibility of placebo assignment.
ICH E10 Choice of Control Group and Related Issues in Clinical Trials; ICH E6(R3) GCP
Frequently asked questions
What is Placebo?
An inactive substance or intervention, indistinguishable in appearance and administration from the investigational product, used as a comparator to isolate the treatment’s pharmacological effect from expectation and natural disease fluctuation. Use of a placebo control raises ethical considerations that must be justified against the availability of established effective therapy.
Which regulations cover Placebo?
ICH E10 Choice of Control Group and Related Issues in Clinical Trials; ICH E6(R3) GCP