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The current central strategy for the development of new and effective painkillers lies in the hypothesis that cellular and / or molecular players in nociception must exists that are not targeted by " classical " analgesics , and therefore researchers have put tremendous efforts into the in - depth analysis of the pathways leading to pain development and maintenance over time .
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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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