Background: The efficacy of methylphenidate for adults with attention-deficit hyperactivity disorder (ADHD) shows wide between-study variability, which yields heterogeneous results in meta-analysis. The reasons for this variability have not been comprehensively investigated.
Objectives: To determine the influence of treatment-related covariates of methylphenidate for adults with ADHD by means of meta-analysis. Clinical and methodological moderators and clinical trial reporting quality were also collected to control for their potential confounding effect.
Methods: We searched for randomized, placebo-controlled clinical trials investigating the efficacy of methylphenidate for adults with ADHD. The study outcome was the efficacy of methylphenidate for reducing ADHD symptom severity. Treatment-related covariates included dose, type of drug-release formulation (formulations with a continuous drug release vs those with a non-continuous drug release), dose regimen (fixed vs flexible) and treatment length. Clinical (presence of co-morbid substance use disorders [SUD]) and methodological (design and rater) covariates were also collected, in addition to clinical trial reporting quality. The standardized mean difference (SMD) was calculated for each study. The analysis of the influence of methylphenidate effect modifiers was performed by means of random-effects meta-regression.
Results: Eighteen studies were included. Dose, type of formulation and SUD appeared to modify the efficacy of methylphenidate in the bivariate analysis. These variables were included in a multivariate meta-regression, which showed that methylphenidate, at an average dose of 57.4 mg/day, delivered by means of non-continuous-release formulations, had a moderate effect on ADHD symptoms compared with placebo (SMD 0.57–0.58). A dose-response relationship was found, indicating that efficacy could be increased by SMD 0.11–0.12 for every 10 mg increment of methylphenidate. Continuous-release formulations and co-morbid SUD appeared to reduce the efficacy of methylphenidate. Nevertheless, the effect of treatment formulation may have been confounded by co-morbid SUD, since all studies using this continuous-release formulation were conducted in dual ADHD-SUD patients. No residual heterogeneity was found.
Conclusions: This study shows that methylphenidate improves ADHD symptoms in adults in a dose-dependent fashion. The efficacy of methylphenidate appears to be reduced in patients with co-morbid SUD. It is unclear whether methylphenidate efficacy is influenced by the type of formulation, because the effect of this covariate is confounded by that of co-morbid SUD.
Methylphenidate ADHD Symptom Standardize Mean Difference Treatment Length Adult ADHD
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This study was funded by grants from the Departament de Salut de la Generalitat de Catalunya, the Agència de Gestió d’Ajuts Universitaris i de Recerca de la Generalitat de Catalunya for Research groups of the Generalitat de Catalunya 2009–2013 SGR 1554 and by la Obra Social “la Caixa” and the Departament de Salut de la Generalitat de Catalunya Programa “PAI-TLP-La Caixa 2009” and “PAI-TLP-La Caixa 2010”.
Dr Xavier Castells, Dr Rosa Bosch and Dr Mariana Nogueira have received lecture fees for participating in conferences organized by Janssen-Cilag. Dr Josep Antoni Ramos-Quiroga and Dr Miguel Casas have received lecture fees for participating in conferences organized by Janssen-Cilag, Laboratios Rubió and Lilly, and consulting fees from Janssen-Cilag. Dr David Rigau and Dr Xavier Vidal report no competing interests.
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