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. 2022 Apr 19;12:6429. doi: 10.1038/s41598-022-09601-2

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© This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2022

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Structures of fentanyls and naloxone. Each circle represents positions which have been abundantly reported to generate illegal fentanyls via chemical modification with various substituents.