In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: OBJECTIVE : The aim of the present study was to investigate the effect of risperidone - induced hyperprolactinemia on trabecular bone mineral density ( BMD ) in children and adolescents .
### Output Text:
OBJECTIVE : The aim of the present study was to investigate the effect of <span class="chemical">risperidone</span> - induced hyperprolactinemia on trabecular bone mineral density ( BMD ) in children and adolescents . 