title: Systematic review: The placebo effect of psychological interventions in the treatment of irritable bowel syndrome.
abstract: OBJECTIVE
  To determine the placebo response rate associated with different types of placebo interventions used in psychological intervention studies for irritable bowel syndrome.
  
  
  METHODS
  Randomized controlled trials comparing psychological interventions (stress management/relaxation therapy (cognitive) behavioral therapy, short-term psychodynamic therapy, and hypnotherapy) for the treatment of adult patients with irritable bowel syndrome (IBS) diagnosed with the Manning or Rome criteria with an adequate placebo control treatment and reporting data on IBS symptom severity were identified by searching PubMed, Embase, the Cochrane Library, CINAHL and PsycINFO databases. Full-text articles that were written in English and published between 1966 and February 2016 in peer-reviewed journals were selected for the present review. Placebo interventions were considered to be adequate if the number of sessions and the amount of time spent with the therapist were the same as in the active treatment. The placebo response rate (PRR) was computed for IBS symptom severity (primary outcome measure) as well as for anxiety, depression and quality of life (secondary outcome measures).
  
  
  RESULTS
  Six studies, with a total of 555 patients met the inclusion criteria. Four studies used an educational intervention, whereas two studies used a form of supportive therapy as the placebo intervention. The PRR for IBS symptom severity ranged from 25% to 59%, with a pooled mean of 41.4%. The relative PRR for the secondary outcome measures ranged from 0% to 267% for anxiety, 6% to 52% for depression 20% to 125% for quality of life. The PRR associated with pharmacological treatments, treatment with dietary bran and complementary medicine ranged from 37.5% to 47%. Contrary to our expectations, the PRR in studies on psychological interventions was comparable to that in studies on pharmacological, dietary and alternative medical interventions.
  
  
  CONCLUSIONS
  The PRR is probably determined to a larger extent by patient-related factors, such as expectations and desire for the treatment to be effective, than the content of the placebo intervention.
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: Carla E
authors.initials: CE
authors.lastname: Flik
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: Laura
authors.initials: L
authors.lastname: Bakker
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: Wijnand
authors.initials: W
authors.lastname: Laan
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: Yanda R
authors.initials: YR
authors.lastname: van Rood
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: André J P M
authors.initials: AJ
authors.lastname: Smout
authors.affiliation: Carla E Flik, Laura Bakker, Wijnand Laan, Niek J de Wit, Department of General Practice, Julius Centre for Health Sciences and Primary Care, University Medical Centre Utrecht, 3508GA Utrecht, The Netherlands.
authors.forename: Niek J
authors.initials: NJ
authors.lastname: de Wit
mesh_terms: D000328:Adult; D000368:Aged; D015928:Cognitive Behavioral Therapy; D005260:Female; D006801:Humans; D043183:Irritable Bowel Syndrome / Q000523:psychology* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D015990:Placebo Effect; D064889:Psychotherapy, Psychodynamic; D011788:Quality of Life; D016032:Randomized Controlled Trials as Topic; D013315:Stress, Psychological; D016896:Treatment Outcome; D055815:Young Adult
keywords: Irritable bowel syndrome; Placebo effect; Psychological interventions; Systematic review