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: These results elucidated ecstasy - related deficits , only some of which might be attributed to cannabis use .
### Output Text:
These results elucidated <span class="chemical">ecstasy</span> - related deficits , only some of which might be attributed to <span class="chemical">cannabis</span> use . 