Involved in the degradation of 4-hydroxybutyrate (PubMed:7851418). Catalyzes the interconversion of gamma-hydroxybutyrate (GHB) and succinic semialdehyde (SSA) (PubMed:31981617). 4-hydroxybutanoate + NAD(+) = H(+) + NADH + succinate semialdehyde Shows competitive inhibition of GHBDH activity by the product succinic semialdehyde, and non-competitive inhibitions by the three other substrate-product combinations. The conversion of GHB to SSA is activated by two different saturating purified nudix hydrolases, B.methanolicus activator ACT and E.coli NudF. The nudix hydrolases do not activate the reverse reaction. kcat is 8.4 sec(-1) with 4-hydroxybutanoate as substrate. kcat is 8.9 sec(-1) with NAD(+) as substrate. Optimum pH is 9.0. Belongs to the iron-containing alcohol dehydrogenase family.