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: The participants recorded menstrual symptoms and possible side - effects at different times ( 0 , 30 , 60 , 120 minutes ) after the first dose of medication on the first day of the cycle , with both drugs .
### Output Text:
The participants recorded menstrual symptoms and possible side - effects at different times ( 0 , 30 , 60 , 120 minutes ) after the first dose of medication on the first day of the cycle , with both drugs . 