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: A policy of unrestricted prescription of appetite suppressants may lead to a high incidence of associated primary pulmonary hypertension .
### Output Text:
A policy of unrestricted prescription of <span class="chemical">appetite suppressants</span> may lead to a high incidence of associated primary pulmonary hypertension . 