title: Different Disclosed Probabilities to Receive an Antiemetic Equally Decrease Subjective Symptoms in an Experimental Placebo Study: To Be or Not to Be Sure.
abstract: OBJECTIVE
  The purpose of this study was to examine whether the disclosed probability of receiving an antiemetic affects nausea.
  
  
  METHODS
  Forty-eight healthy participants (mean [SD] age, 26.8 [5.4] years; 50% female) were exposed to 5 × 2 minutes of nauseogenic body rotations on 2 days. On day 2, participants were randomized to 3 experimental groups that were given different instructions concerning the probability of receiving an antiemetic remedy (100%, 50%, or 0% probability), whereas all received an inert substance. Subjective symptoms, behavioral (rotation tolerance) measures, and physiologic (electrogastrogram) measures of nausea were assessed and mediator and moderator analyses performed for effects of expectations and psychological characteristics on outcomes.
  
  
  RESULTS
  Disclosed probabilities of both 100% and 50% significantly reduced subjective symptoms of nausea in an equal manner compared with the 0% probability group from day 1 to day 2. This effect was found for neither rotation tolerance nor myoelectric gastric activity. Expectations and psychological characteristics did not affect the results found. Post hoc analyses revealed that women only seem to be susceptible to this placebo effect.
  
  
  CONCLUSIONS
  Nausea is susceptible to placebo effects independent of the disclosed probability of receiving a drug and of explicit expectations. In line with placebo research, this effect is probably attributable to central mechanisms, and it is speculated that it could be related to the reward circuitry and social interactions.
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tübingen, Tübingen, Germany. Electronic address: katja.weimer@uni-tuebingen.de.
authors.forename: Katja
authors.initials: K
authors.lastname: Weimer
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tübingen, Tübingen, Germany; Institute of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Horing
authors.affiliation: Department of Psychology, Clemson University, Clemson, South Carolina.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Muth
authors.affiliation: Department of Psychology, Clemson University, Clemson, South Carolina; Department of Psychology, Eastern Connecticut State University, Willimantic, Connecticut.
authors.forename: Jenna L
authors.initials: JL
authors.lastname: Scisco
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Sibylle
authors.initials: S
authors.lastname: Klosterhalfen
authors.affiliation: Department of Psychosomatic Medicine and Psychotherapy, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Paul
authors.initials: P
authors.lastname: Enck
mesh_terms: D000328:Adult; D000932:Antiemetics / Q000008:administration & dosage* / Q000627:therapeutic use; D005260:Female; D006801:Humans; D008297:Male; D009325:Nausea / Q000188:drug therapy / Q000523:psychology*; D015990:Placebo Effect; D011336:Probability; D012399:Rotation; D055815:Young Adult
chemical_list: D000932:Antiemetics
keywords: expectancy; motion sickness; nausea; placebo effect; uncertainty