Placebo and Nocebo Responses in Randomized, Controlled Trials of Medications for ADHD: A Systematic Review and Meta-Analysis

Abstract

Background: The nature and magnitude of placebo and nocebo responses to ADHD medications is unclear. The extent to which response to active medications and placebo are inter-correlated has not been explored. Methods: We searched scientific literature until June 26, 2019 for published/unpublished double-blind, randomised placebo-controlled trials (RCTs) of ADHD medications in children, adolescents and adults. Authors and drug manufacturers were contacted for additional information. We assessed placebo effects on efficacy and nocebo effects on tolerability outcomes using aggregate data from trials and random-effects meta-analysis. We assessed the association of study design and patient features with placebo/nocebo response. Findings: We analysed 128 RCTs and found significant and heterogenous placebo effects for all efficacy outcomes, with no publication bias. We found nocebo effects on some tolerability outcomes. Apart from self-ratings, efficacy outcomes from other raters showed significant positive correlations between the baseline to endpoint placebo effects and the baseline to endpoint drug effects, suggesting that response to placebo and ADHD medications are influenced by similar non-specific factors. Baseline severity and type of rating scale influenced the magnitude of placebo response. Interpretation: Placebo effects are highly significant and response to placebo and ADHD medications are correlated, suggesting that shared non-specific factors influence response to both placebo and active medication. Although ADHD medications are superior to placebo, and placebo treatment in clinical practice is not feasible, clinicians should attempt to incorporate factors associated with placebo effects into clinical care, and future studies should explore how such effects influence response to medication treatment. Funding Statement: This was not a funded study. Declaration of Interests: In the past year, Dr. Faraone received income, potential income, travel expenses continuing education support and/or research support from Takeda, OnDosis, Tris, Otsuka, Arbor, Ironshore, Rhodes, Akili Interactive Labs, Enzymotec, Sunovion, Supernus and Genomind. With his institution, he has US patent US20130217707 A1 for the use of sodium-hydrogen exchange inhibitors in the treatment of ADHD. He also receives royalties from books published by Guilford Press: Straight Talk about Your Child’s Mental Health, Oxford University Press: Schizophrenia: The Facts and Elsevier: ADHD: Non-Pharmacologic Interventions. He is Program Director of www.adhdinadults.com. In the past year, Dr. Newcorn is/has been an advisor and/or consultant for Adlon Therapeutics, Arbor, Eisai, NLS, OnDosis, Rhodes, Shire/Takeda, and Supernus. He was a DSMB member for Pfizer and Sunovion, and received research funds from Otsuka, Shire and Supernus. He also has received speaker fees from Shire/Takeda for disease-state presentations and served as a consultant for the US National Football League. Dr. Cipriani has received research and consultancy fees from INCiPiT (Italian Network for Paediatric Trials), CARIPLO Foundation and Angelini Pharma. Dr. Brandeis serves as an unpaid scientific consultant for an EUfunded neurofeedback trial. Anna Kaiser reports has no financial disclosures. Sarah Hohmann has no financial disclosures. Dr. Hage received conference support, speaker´s fee and/or served in an advisory role for Shire/Takeda and Lily. He was involved as investigator in clinical trials by Shire, Janssen-Cilag, Otsuka, Sunovion, Servier, Lundbeck, Takeda,Nuvelution, Gedeon Richter, and Emalex. The present work is unrelated to the above relationships. Dr. Cortese declares reimbursement for travel and accommodation expenses from the Association for Child and Adolescent Central Health (ACAMH) in relation to lectures delivered for ACAMH, Canadian ADHD Resource Alliance (CADDRA), British Association of Psychopharmacology (BAP), and from Healthcare Convention for educational activity on ADHD.