Parameter Sleep eﬃciency (%) Sleep latency (h : min) Actual sleep time (%) Actual wake time (%) Mean activity score Movement and fragmentation index Number of minutes moving Number of minutes immobile 80.4 0 : 4 87.8 12.2 12.1 31.2 14.1 86.0 2 Case Reports in Medicine Table 1: Mean values for actigraphic parameters before and during treatment with methylphenidate. Daily dosage and duration of treatment with methylphenidate 0 mg for 16 days 18 mg for 6 days 36 mg for 5 days 69.0 1 : 2 86.7 13.4 13.5 34.9 15.7 84.4 67.4 1 : 1 80.0 20.0 26.5 44.8 22.3 77.7 Hospital, Helsinki, Finland. All the patients volunteered for the study and signed an informed consent after the protocol had been fully explained and before any procedure was performed. Here, we present a case report of one of the study participants, a 40-year-old man. He was recently diagnosed as having ADHD, with no medication prior to the study. The dosage was at start one tablet (18 mg of methylphenidatehydrochloride) in the morning, and after six days of medication the daily dose was increased up to two tablets (36 mg of methylphenidatehydrochloride) in the morning. Concomitant psychotropic medication was not allowed during the study. The daily rest-activity cycles were continuously recorded with a wrist-worn accelerometer (actigraph). It gives information about the duration and quality of sleep and the level of physical activity. He wore the accelerometer on his nondominant hand all the time, except during bathing or swimming, for 16 days before starting the treatment with methylphenidate and for 11 days (18 mg for 6 days followed by 36 mg for 5 days) during the active treatment. The actigraphic variables used for the analysis included sleep eﬃciency (the percentage of time spent asleep whilst in bed), sleep latency (the time delay between going to bed and falling asleep), actual sleep time (the percentage of time spent in bed in a sleep), actual wake time (the percentage of actual time spent awake in bed), mean activity score (the average value of the activity counts per epoch over the assumed sleep period), movement and fragmentation index (indicates the restlessness of the sleep), number of minutes moving (the total number of minutes moving during sleep), and number of minutes immobile (the total number of minutes immobile). The data were analyzed with the software provided by the manufacturer (The Actiwatch Sleep Analysis 2001, version 1.19). 3. Results The patient’s response to methylphenidate was clinically rated as good. In addition to alleviation of his ADHD symp- toms, his bruxism and nail-biting activities were reduced. However, he became increasingly more talkative and excited during the treatment with methylphenidate. He reported that his subjective quality of sleep was decreased, which was conﬁrmed in the actigraphic recordings (Table 1). After dou- bling the methylphenidate dosage from 18 mg to 36 mg per day, he became more impulsive. He described experiencing a totally new understanding of life and some kind of bonding with the universe. He had rapid mood swings during the days. He felt very energetic and was exceptionally active. The diagnosis of a manic episode (substance-induced) was assessed, when he had an appointment (per study protocol) with one of the authors (PT). His wife was met during the appointment and conﬁrmed the change in activity and behavior. The patient was excluded from the study and his treatment with methylphenidate stopped immediately. His manic symptoms disappeared completely during the following days, and no mood-stabilizing medication was needed. In the actigraphic recordings, the quality and the duration of sleep were reduced during the treatment with methylphenidate (Table 1). Sleep eﬃciency was reduced in proportion to the methylphenidate dose. Sleep latency was increased, actual sleep time was decreased, and actual wake time was increased during the treatment. All the activity variables indicated that sleep became increasingly more restless as the methylphenidate dose increased. 4. Conclusions Insomnia is known to be a potential adverse eﬀect of psychostimulants and may trigger manic episodes [8, 9]. Patients with mood disorder in particular are vulnerable to sleep disruption, and among bipolar patients with the comorbid ADHD the rate of the stimulant-associated hypo- mania or mania is as high as 40% [10–15]. Our patient had no prior history of depressive, hypomanic or manic episodes. During a follow-up of three years, our patient has experienced no further episodes of mood disorder, although he is still being treated with methylphenidatehydrochloride (mainly short-acting tablets, 20–25 mg/day). However, he has reported that occasionally, after the use of longer-acting methylphenidate tablets for three or more consecutive days, insomnia returns and his symptoms start to resemble those experienced during the manic episode. Clinical experience is that disruptions in sleep often predict onset of mood episodes, both mania and depression. Here, methylphenidate disrupted sleep and induced mania- like symptoms in an adult patient with ADHD, but no