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In the original print version of this manuscript, Fig. 1 contained several errors. In Fig. 1b, a double bond is missing in the structures of heroin, 6-acetylmorphine and morphine. In Fig. 1c, the N-alkyl group is one carbon too short in the naloxone methiodide structure. In addition, the stereochemistry of the structures in Fig. 1b and of naloxone methiodide in Fig. 1c was incorrect. The errors occurred during preparation of these panels for publication, and the authors apologize for any inconvenience this may have caused. Corrected versions of both panels are reproduced here.