Large interindividual differences exist in the presence and extent of placebo responses in both experimental and clinical studies, but little is known about possible predictors of these responses. We employed a behaviorally conditioned immunosuppression paradigm in healthy men to analyze predictors of learned placebo responses. During acquisition, the subjects received either the immunosuppressant cyclosporin A (n = 32) or a placebo (n = 14) (unconditioned stimuli (US)) together with a novel-tasting drink (conditioned stimulus (CS)). During evocation, the subjects were reexposed to the CS alone. In responders (n = 15), the CS alone caused a significant inhibition of interleukin (IL)-2 production by anti-CD3-stimulated peripheral blood T cells, closely mimicking the drug effect. Nonresponders (n = 17) did not show responses different from those of the controls. Multiple-regression analyses showed that baseline IL-2, plasma noradrenaline, and state anxiety predicted nearly 60% of the variance in the conditioned IL-2 response. These data provide first evidence for putative biological and psychological predictors of learned placebo responses.

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