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: However , it is currently unknown if the acute toxic dosage of METH also causes a long - lasting depressive phenotype and persistent monoaminergic deficits .
### Output Text:
However , it is currently unknown if the acute toxic dosage of <span class="chemical">METH</span> also causes a long - lasting depressive phenotype and persistent monoaminergic deficits . 