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. May be involved in protection of liver against the toxic and carcinogenic effects of AFB1, a potent hepatocarcinogen (By similarity). 4-hydroxybutanoate + NADP(+) = H(+) + NADPH + succinate semialdehyde Inhibited by citrate, succinate and tartrate. Homodimer. Expressed in liver, kidney, testis and brain with low levels in skeletal muscle, spleen, heart and lung. Belongs to the aldo/keto reductase family. Aldo/keto reductase 2 subfamily.