Nicotinamide adenine dinucleotide phosphate, abbreviated NADP[1][2] or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source').

[3] NADP+ differs from NAD+ by the presence of an additional phosphate group on the 2' position of the ribose ring that carries the adenine moiety.

ADP-ribosyl cyclase allows for synthesis from nicotinamide in the salvage pathway, and NADP+ phosphatase can convert NADPH back to NADH to maintain a balance.

The major source of NADPH in animals and other non-photosynthetic organisms is the pentose phosphate pathway, by glucose-6-phosphate dehydrogenase (G6PDH) in the first step.

[3] Ferredoxin–NADP+ reductase, present in all domains of life, is a major source of NADPH in photosynthetic organisms including plants and cyanobacteria.

It has functions in accepting electrons in other non-photosynthetic pathways as well: it is needed in the reduction of nitrate into ammonia for plant assimilation in nitrogen cycle and in the production of oils.

[7] The isocitrate dehydrogenase mechanism appears to be the major source of NADPH in fat and possibly also liver cells.

[3] Another carbon metabolism-related pathway involved in the generation of NADPH is the mitochondrial folate cycle, which uses principally serine as a source of one-carbon units to sustain nucleotide synthesis and redox homeostasis in mitochondria.

Mitochondrial folate cycle has been recently suggested as the principal contributor to NADPH generation in mitochondria of cancer cells.

[10] NADPH provides the reducing agents, usually hydrogen atoms, for biosynthetic reactions and the oxidation-reduction involved in protecting against the toxicity of reactive oxygen species (ROS), allowing the regeneration of glutathione (GSH).