IntroductionAttention deficit/hyperactivity disorder (ADHD) affects 5–6% of adults. Methylphenidate challenge is used to test functions such as concentration. Therapeutic drug monitoring (TDM) identifies optimal drug ranges in plasma.Objectives/AimsWe aimed to: assess the clinical impact of the drug challenge in adults with ADHD; analyze the relationship with the drug plasma levels after the challenge; identify predictors of the challenge's clinical impact.MethodsIn 2015–2016, we recruited 45 consecutive adult DSM-5 ADHD outpatients (mean age ± SD = 35.3 ± 2.1 years; females = 64.4%) at the Bolzano hospital department of psychiatry. Before and after administration of methylphenidate 10 mg, we measured concentration, impulsivity, tension, and general well-being with a VAS and an interview. After two hours, TDM was performed. Deltas were calculated for pre-/post-challenge measures. Correlations were measured with Pearson's r/point-biserial coefficient. A generalized linear mixed model estimated the size of association between tension/general well-being improvement and patient characteristics.ResultsAfter the challenge, the mean improvement ± SD was 24 ± 22 for concentration, 17 ± 23 for impulsivity, 21 ± 28 for tension, 16 ± 24 for general well-being. The mean TDM ± SD was 4.6 ± 0.5 ng/mL. A negative correlation between TDM, tension (P = 0.009), and general well-being (P = 0.028) after the challenge emerged: higher drug plasma levels relate to less tension and greater general well-being. At the GLMM the main predictor for tension/general well-being improvement was psychopharmacological treatment (P = 0.011/P = 0.05, respectively). Older age and difficult tasks prevented improvement.ConclusionsMethylphenidate challenge had a positive effect on all patients’ performance. TDM values were lower than literature ones, although the latter are usually obtained after the administration of methylphenidate 20 mg.Disclosure of interestThe authors have not supplied their declaration of competing interest.