Placebo

A treatment designed to lack the specific active component being tested for a condition. Its effects can arise from expectations, treatment context, and natural changes in symptoms.

Placebo effect: A change in symptoms or other outcomes associated with receiving a placebo or its treatment context. This is the outcome commonly attributed to placebo treatment, though it is not always caused by the placebo itself.
Randomized controlled trial: A study that randomly assigns participants to interventions to compare their effects. Random assignment helps estimate whether an active treatment outperforms a placebo.
Placebo-controlled trial: A clinical trial that compares an intervention with a placebo group. This design tests whether an intervention produces benefits beyond those seen with placebo.
Active control: A comparison treatment with an established active ingredient or effect. Unlike a placebo, an active control provides a specific therapeutic intervention.
Expectancy theory: An account of how expectations shape perception, behavior, and bodily responses. Expectations about relief can influence symptoms after placebo treatment.
Blinding (clinical trials): A trial procedure that keeps participants or investigators unaware of assigned treatments. Blinding limits expectations from revealing who received the placebo.
Open-label placebo: A placebo given with disclosure that it contains no active treatment ingredient. Studies test whether some placebo-associated benefits occur even without deception.
Usual care: The standard treatment or management ordinarily provided in a clinical setting. Trials may compare an intervention with routine care rather than an inactive treatment.
Classical conditioning: A learning process in which a stimulus comes to elicit a response after being paired with another stimulus. Past pairings between treatment cues and relief can condition responses to placebos.
Placebo control: A comparison group given an inactive treatment in a clinical study. A placebo control provides the comparison needed to estimate a treatment's specific effect.

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