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: METHOD : Seventy - six participants ( 21 nonusers , 29 light ecstasy - polydrug users , 26 heavy ecstasy - polydrug users ) completed a substance use inventory and measures of psychological distress at baseline , then two consecutive days of cortisol sampling ( on awakening , 30 min post awakening , between 1400 and 1600 hours and pre bedtime ) .
### Output Text:
METHOD : Seventy - six participants ( 21 nonusers , 29 light <span class="chemical">ecstasy</span> - polydrug users , 26 heavy <span class="chemical">ecstasy</span> - polydrug users ) completed a substance use inventory and measures of psychological distress at baseline , then two consecutive days of <span class="chemical">cortisol</span> sampling ( on awakening , 30 min post awakening , between 1400 and 1600 hours and pre bedtime ) . 