Background: Stimulants are the most effective drugs for attention-deficit/hyperactivity disorder (ADHD) symptoms. The purpose of this study was to explore the intervention effect of methylphenidate, a commonly used stimulant, on cognitive performance in ADHD children and whether the effect is associated with age, sex, different subtypes of ADHD, and drug dosage.
Methods: Children with ADHD were divided into the following subtypes: combined type, predominantly inattentive type, and hyperactive/impulsive type. The intervention group consisted of 159 children treated with methylphenidate, and the control group consisted of 78 untreated patients. All 237 subjects were given a Wechsler Intelligence Scale for Children--Revised test at baseline, and 6 months later, they were retested. The scores of Verbal Intelligence Quotient (IQ) test, Performance IQ (PIQ) test, Full Scale IQ (FSIQ) test, and subtests were compared before and after the intervention.
Results: At baseline, scores were not statistically different between the 2 groups. After 6 months, PIQ and FSIQ scores of intervention group were higher than those of the control group (P < 0.05). Compared with baseline scores, the intervention group, but not the control group, showed significant increases in Verbal IQ (P < 0.05), PIQ (P < 0.01), and FSIQ (P < 0.01). In the intervention group, the 5 subtests scores of PIQ improved significantly (P < 0.01). In the control group, none of the scores from the subtests showed statistical differences. Furthermore, there was no statistical difference between the change of IQ scores and children's age, sex, different subtypes of ADHD, and drug dosage.
Conclusions: Methylphenidate can enhance cognitive performance in ADHD patients thus evaluating their IQ scores, although the effect size seems to be relatively small. The result should not be indicated as an increase in intelligence.