3α,21-Dihydroxy-5α-pregnan-20-one-d 3 is the deuterium labeled 3α,21-Dihydroxy-5α-pregnan-20-one. 3α,21-Dihydroxy-5α-pregnan-20-one (THDOC), an endogenous neurosteroid, is a positive modulator of GABAA receptors. 3α,21-Dihydroxy-5α-pregnan-20-one potentiates neuronal response to low concentrations of GABA at α4β1δ GABAA receptors in vitro.