Drug holidays may not affect processing speed while they may reduce beneficial effects on resistance to interference among children with treated with methylphenidate: a single-center, prospective study.

Objective: This study aimed to investigate the effects of drug holidays during summer vacations among children with attention deficit/hyperactivity disorder (ADHD) who were treated with methylphenidate in terms of ADHD symptoms and executive functions.
Methods: The study was a prospective cohort study that includes pre-treatment, post-treatment and post-drug holiday evaluations. ADHD symptom severity was evaluated with the Clinical Global Impression Scale (CGI), the Conners' Parental Rating Scale-Short Form (CPRS) and the Conners' Teacher Rating Scale- Short Form (CTRS). The Stroop Color Word Test- TBAG Form (SCWT) was used to evaluate executive functions. Fifty-one patients participated in the study according to the inclusion and exclusion criteria. Methylphenidate (MPH) was started at 0.5 mg/kg/day and titrated weekly to a maximum of 1.2 mg/kg/day. During the follow-up period, 22 (43.0%) of the patients stopped treatment.
Results: Completion times for all SCWT subtests were significantly reduced after treatment ( p  < 0.001, p  = 0.002, p  < 0.001, p  = 0.002, p  < 0.001; respectively). Mean number of corrections in SCWT-3 and mean number of errors as well as corrections in SCWT-5 significantly reduced after treatment ( p  = 0.047, p  = 0.005, p  = 0.007; respectively). Mean number of corrections in SCWT-3 and mean number of errors in SCWT-5 increased significantly after drug holiday compared to post-treatment ( p  = 0.032 and p  = 0.037; respectively).
Conclusion: Our results suggest that psychomotor speed and resistance to interference improved in children with ADHD receiving methylphenidate treatment. Drug holidays did not affect psychomotor speed while beneficial effects on resistance to interference were reduced with drug holidays.