This enzyme is required for electron transfer from NADP to cytochrome P450 in microsomes. It can also provide electron transfer to heme oxygenase and cytochrome B5 (By similarity). Involved in the biosynthesis of the antimalarial endoperoxide artemisinin (By similarity). Acts as a redox partner for CYP71AV1 which catalyzes the conversion of amorphadiene to more oxygenated products (By similarity). NADPH + 2 oxidized [cytochrome P450] = H(+) + NADP(+) + 2 reduced [cytochrome P450] Binds 1 FAD per monomer. Binds 1 FMN per monomer. 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 NADPH--cytochrome P450 reductase family. In the N-terminal section; belongs to the flavodoxin family. In the C-terminal section; belongs to the flavoprotein pyridine nucleotide cytochrome reductase family.