Psychiatric illness in the paediatric population is increasing and the weight effect of medications for these problems is often unclear. A comprehensive literature search was undertaken to identify studies reporting weight in relation to antipsychotic and antidepressant use in children and adolescents. From 636 articles, 42 were selected for review. Selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs) do not cause weight gain and may lead to improvements in weight status over the short, but not, long term. Antipsychotics were generally associated with weight gain. In drug comparison studies, risperidone had a larger weight gain effect than lithium, divalproex sodium and pimozide. Studies assessing the weight-protective effects of augmentation therapy with metformin or topiramate show less weight gain with addition of these agents. In conclusion, prescribing of SSRIs and SNRIs may be associated with improvements in weight status in children and adolescents but trials assessing their use in obesity, outside of established psychiatric illness, are limited and still experimental. Youth prescribed antipsychotic medication should be monitored for exaggerated weight gain and in those where obesity is a pre-existing concern agents other than olanzapine, clozapine and risperidone may be advantageous.