In enzymology, a morphine 6-dehydrogenase (EC 1.1.1.218) is an enzyme that catalyzes the chemical reaction

morphine + NAD(P)⁺ ${\displaystyle \rightleftharpoons }$ morphinone + NAD(P)H + H⁺

The 3 substrates of this enzyme are morphine, NAD⁺, and NADP⁺, whereas its 4 products are morphinone, NADH, NADPH, and H⁺.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-OH group of donor with NAD⁺ or NADP⁺ as acceptor. The systematic name of this enzyme class is morphine:NAD(P)⁺ 6-oxidoreductase. Other names in common use include naloxone reductase, and reductase, naloxone. This enzyme participates in alkaloid biosynthesis i. This enzyme has at least one effector, Mercaptoethanol.

• Yamano S, Kageura E, Ishida T, Toki S (1985). "Purification and characterization of guinea pig liver morphine 6-dehydrogenase". J. Biol. Chem. 260 (9): 5259–64. PMID 2580834.
• Yamano S, Nishida F, Toki S (1986). "Guinea-pig liver morphine 6-dehydrogenase as a naloxone reductase". Biochem. Pharmacol. 35 (23): 4321–6. doi:10.1016/0006-2952(86)90712-4. PMID 3539118.