In enzymology, a geissoschizine dehydrogenase (EC 1.3.1.36) is an enzyme that catalyzes the chemical reaction

geissoschizine + NADP⁺ 4,21-didehydrogeissoschizine + NADPH

Thus, the two substrates of this enzyme are geissoschizine and NADP⁺, whereas its two products are 4,21-didehydrogeissoschizine and NADPH.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the CH-CH group of donor with NAD+ or NADP+ as acceptor. The systematic name of this enzyme class is geissoschizine:NADP+ 4,21-oxidoreductase. This enzyme participates in indole and ipecac alkaloid biosynthesis.

• Pfitzner A, Stockigt J (1982). "Partial-purification and characterization of geissoschizine dehydrogenase from suspension-cultures of Catharanthus roseus". Phytochemistry. 21: 1585–1588. doi:10.1016/s0031-9422(82)85022-x.