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: Ecstasy users performed significantly worse in learning and memory compared to controls and cannabis users .
### Output Text:
<span class="chemical">Ecstasy</span> users performed significantly worse in learning and memory compared to controls and <span class="chemical">cannabis</span> users . 