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: Unfortunately , the results from human research investigating its psychological effects have been inconsistent .
### Output Text:
Unfortunately , the results from human research investigating its psychological effects have been inconsistent . 