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: Menstrual abnormalities ( 79 % ) , weight gain ( 60 % ) , muscle cramps / myalgias ( 40 % ) , and transaminase elevations ( 40 % ) were the most common adverse reactions .
### Output Text:
Menstrual abnormalities ( 79 % ) , weight gain ( 60 % ) , muscle cramps / myalgias ( 40 % ) , and transaminase elevations ( 40 % ) were the most common adverse reactions . 