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 effect of mazindol on GH secretion was estimated indirectly by comparing the postabsorptive IGF - I levels obtained following 3 , 6 , 9 , and 12 months in the mazindol treated to those in the placebo groups .
### Output Text:
The effect of <span class="chemical">mazindol</span> on GH secretion was estimated indirectly by comparing the postabsorptive IGF - I levels obtained following 3 , 6 , 9 , and 12 months in the <span class="chemical">mazindol</span> treated to those in the placebo groups . 