Involved in the biosynthesis of the antimalarial endoperoxide artemisinin (PubMed:18495659, PubMed:27488942). Catalyzes the double bond reduction of artemisinic aldehyde to produce (11R)-dihydroartemisinic aldehyde (PubMed:18495659). Also able to reduce 2-cyclohexen-1-one into cyclohexanone to a lesser extent (PubMed:18495659). (11R)-dihydroartemisinic aldehyde + NADP(+) = (+)-artemisinic aldehyde + H(+) + NADPH kcat is 2.6 sec(-1) with artemisinic aldehyde as substrate. kcat is 1.8 sec(-1) with 2-cyclohexen-1-one as substrate. kcat is 0.86 sec(-1) with (+)-carvone as substrate. kcat is 1.3 sec(-1) for the NADH-dependent reduction of artemisinic aldehyde. Optimum pH is 7.5. Sesquiterpene biosynthesis. Expression at relatively high level in glandular trichomes, and at lower level in leaves and flower buds (PubMed:18495659). Weakly expressed in roots (PubMed:18495659). Expressed both in apical and sub-apical cells of glandular secretory trichomes (PubMed:22195571, PubMed:19664791). Also present in non-glandular trichome cells (PubMed:30851440). Artemisinin and derivatives (e.g. artesunate), are antimalarial drugs due to their endoperoxidase properties; they also display multiple pharmacological actions against inflammation,viral infections, and cell and tumor proliferation (PubMed:32514287, PubMed:32405226). Artesunate may be a promising treatment for COVID-19 mediated by the severe acute respiratory syndrome coronavirus 2 (2019-nCoV) (SARS-CoV-2) because of its anti-inflammatory activity, NF-kappaB (nuclear factor kappa B)-coronavirus effect and chloroquine-like endocytosis inhibition mechanism (PubMed:32514287, PubMed:32405226). Belongs to the NADH:flavin oxidoreductase/NADH oxidase family.