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: She reported her use of methamphetamine for five years and had not experienced any major carious episodes before she started using the drug .
### Output Text:
She reported her use of <span class="chemical">methamphetamine</span> for five years and had not experienced any major carious episodes before she started using the drug . 