A significant response to placebo in randomized controlled trials of treatments for cancer‐related fatigue (CRF) had been reported. A retrospective study was conducted to determine the frequency and predictors of response to placebo effect and nocebo effects in patients with CRF treated in those trials.

The records of 105 patients who received placebo in 2 previous randomized clinical trials conducted by this group were reviewed. The proportion of patients who demonstrated clinical response to fatigue, defined as an increase in Functional Assessment of Chronic Illness Therapy‐Fatigue score of ≥7 from baseline to Day 8, and the proportion of patients with a nocebo effect, defined as those reporting >2 side effects, were determined. Baseline patient characteristics and symptoms recorded using the Edmonton Symptom Assessment Scale (ESAS) were analyzed to determine their association with placebo and nocebo effects.

Fifty‐nine (56%) patients had a placebo response. Worse baseline anxiety and well‐being subscale score (univariate) and well‐being (multivariate) were significantly associated with placebo response. Commonly reported side effects were insomnia (79%), anorexia (53%), nausea (38%), and restlessness (34%). Multivariate analysis indicated that worse baseline (ESAS) sleep, appetite, and nausea were associated with increased reporting of the corresponding side effects.

Greater than half of advanced cancer patients enrolled in CRF trials had a placebo response. Worse baseline physical well‐being score was associated with placebo response. Patients experiencing specific symptoms at baseline were more likely to report these as side effects of the medication. These findings should be considered in the design of future CRF trials. Cancer 2010. © 2009 American Cancer Society.