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 findings suggest that curcumin can be considered as a potential safe and effective adjuvant to phenobarbitone and carbamazepine therapy in preventing cognitive impairment associated with these drugs .
### Output Text:
The findings suggest that <span class="chemical">curcumin</span> can be considered as a potential safe and effective adjuvant to <span class="chemical">phenobarbitone</span> and <span class="chemical">carbamazepine</span> therapy in preventing cognitive impairment associated with these drugs . 