Discussion
ADHD
The aim of the present study was to examine the effects of one single-dose IR-MPH compared to one single-dose placebo on performance in ADHD core symptoms during clinical assessment with continuous performance test. In a double-blinded crossover procedure, adults were administered IR-MPH in one session and placebo in the other in randomized order. To our knowledge this is the first study that has examined one single-dose IR-MPH compared to one single-dose placebo in clinical trials with the QbTest in adult patients.The results of our study show significant improvements in all three core symptoms, and all included parameters except commission error, after intake of one single-dose IR-MPH. Our data are in accordance with results from an earlier study in children [We also noted significant improvements in the cardinal parameter QbInattention and the parameters Reaction Time, Reaction Time Variation and Omission Error after intake of placebo. When we analysed the two groups separately, adults in the placebo/MPH group performed significantly better in the cardinal parameter QbInattention on the first trial day, compared to the second trial day. Adults in the MPH/placebo group also improved their performance in the cardinal parameter QbInattention when given placebo, despite they were verbally informed about the presence of a placebo in one of the trial days. The difference in performance between baseline and placebo may be due to high treatment expectations. According to expectancy theory, placebo effects are mediated by explicit expectancies [Commission error showed a low effect size in the study probably because this measure has lower sensitivity for adults with ADHD compared to children. In earlier studies, higher rates of Commission Error were found in children compared to adolescents and adults [Further, we hypothesized the placebo response would be higher in the beginning and decrease at the end of the test, since adults with ADHD often have difficulties in focusing during a longer period. When we analysed changes in the adults´ performance in the five-minute Quartiles Q2, Q3 and Q4, we noted significantly increases in the activity measures during baseline from Q2 to Q4. Similar results have been reported by Lis et al. [