Patients receiving second-generation antipsychotics (SGAs) may experience secondary metabolic effects such as weight gain, as well as changes in lipid and glucose metabolism. These effects are well documented in adults; however, fewer studies are available concerning their occurrence and their evolution in children and adolescents.The aim of this study was to determine if there is an age-dependent variation in the metabolic effects of SGAs in a drug-naïve population.Charts of 232 French Canadian patients participating in a program monitoring the metabolic effects of SGAs were retrospectively reviewed. A total of 85 SGA-naïve patients were selected, including 58 youths and 27 adults. Changes, relative to baseline, in weight, body mass index, lipid metabolism (total cholesterol, low-density lipoprotein, high-density lipoprotein, and triglyceride), and fasting blood glucose were assessed, with follow-up at 3, 6, 12, and 24 months.With respect to weight gain, in both the youth and adult groups, body mass index significantly increased from baseline at 3 months (10.1% [p < 0.0001] and 12.2% [p < 0.0001], respectively) and 6 months (11.8% [p < 0.0001] and 13.1% [p < 0.0001], respectively). With respect to lipid metabolism, in the youth group, there was no significant change. In the adult group, there was a significant increase at 3 and 6 months in total cholesterol (24.0% [p = 0.004] and 24.1% [p = 0.0006], respectively), low-density lipoprotein (26.8% [p = 0.019] and 30.1% [p = 0.010], respectively), and high-density lipoprotein (10.2% [p = 0.04] and 17.1% [p = 0.005], respectively). There was no significant change in triglyceride and glucose metabolism in both groups.Our results confirm the age-independent effects of SGA on weight gain. However, more data are needed to explore the age effect on glucose and lipid metabolism.