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Butyr-fentanyl , often abbreviated as B-F , or Butyrylfentanyl ( not to be confused with 3-methylfentanyl ) is a potent short-acting synthetic opioid analgesic drug .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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