Catalyzes the NADPH-dependent reduction of succinic semialdehyde to gamma-hydroxybutyrate. May have an important role in producing the neuromodulator gamma-hydroxybutyrate (GHB). Has broad substrate specificity. Can reduce the dialdehyde protein-binding form of aflatoxin B1 (AFB1) to the non-binding AFB1 dialcohol. Acts as a 2-carboxybenzaldehyde reductase. 4-hydroxybutanoate + NADP(+) = H(+) + NADPH + succinate semialdehyde Has a low KM for succinic semialdehyde. Homodimer. Heterodimer with AKR7A1. Its association with the Golgi stack may facilitate secretion of GHB. With 4-nitrobenzaldehyde as substrate, it exhibits a substantially greater specific activity with NADPH than with NADH. Conversely, it has a 1.8-fold higher activity towards succinic semialdehyde with NADH than with NADPH. Belongs to the aldo/keto reductase family. Aldo/keto reductase 2 subfamily.