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All currently available antidepressant medications have stemmed from study of the mechanisms of serendipitously discovered drugs , and only 30 - 50 % of patients exhibit remission and frequently at least 3 - 4 weeks are required for manifestation of significant therapeutic effects .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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