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. Author manuscript; available in PMC: 2022 Apr 27.
Published in final edited form as: Pharmacol Biochem Behav. 2021 Jul 21;208:173242. doi: 10.1016/j.pbb.2021.173242

Fig. 1.

Fig. 1.

Chemical structures of (1) morphine, (2) fentanyl, (3) beta-methylfentanyl, (4) para-methylfentanyl, (5) para-methoxyfentanyl, (6) fentanyl carbamate, (7) 3-furanylfentanyl, (8) phenylfentanyl, and (9) beta′-phenylfentanyl.