Objective: To determine whether long-term treatment of attention deficit hyperactivity disorder (ADHD) with methylphenidate influences the growth in height and weight of children.
Methods: Analyses were performed on 146 school age children (126 boys) diagnosed as ADHD and treated with methylphenidate [0.27-0.64 mg/(kg.day)] for methylphenidate group and 29 children with ADHD who did not receive any medication for ADHD (controls). These children were followed-up for 2-4 years. Changes in height and weight after long-term treatment with methylphenidate were recorded and the factors affecting growth of height, weight, and height velocity were analyzed.
Results: The change of difference between patients' height and mean height in methylphenidate group and controls was (-1.86 +/- 0.82) cm (paired t test, t = 27.335, P < 0.001) and (-0.26 +/- 0.51) cm (P < 0.05), respectively; the change of height standard deviation score (SDS) in methylphenidate group and controls was -0.14 +/- 0.23 SD (paired t test, t = 7.326, P < 0.001) and +0.05 +/- 0.10 SD (P < 0.05), respectively. When the height change and height SDS change in methylphenidate group and controls were compared by using independent-samples T-test, the t value was -10.078 and -4.262 respectively, P for both was < 0.001. Both of bivariate correlation analysis and stepwise multiple-regression analysis indicated that the duration of treatment contributed significantly to the variance in change of height (P < 0.001); but age, sex, DSM-IV type, NJ22 degree and dose of methylphenidate did not contribute significantly to the variance of height. The mean height velocity from 1st to 4th year was 4.28 cm/year, 4.90 cm/year, 4.98 cm/year and 4.95 cm/year, respectively. With Friedman test, Chi-square = 253.673, P < 0.001. The change of difference of patients' weight to weight for height after methylphenidate was (-0.14 +/- 1.25) kg (paired t test, t = 1.326, P > 0.05).
Conclusion: Small but significant deceleration of height velocity is the identified long-term side effect of methylphenidate, the magnitude of height deficit is related to duration of treatment. The height velocity was significantly attenuated in the first year. Methylphenidate had no significant influence on weight.