5β-Dihydroprogesterone (5β-DHP) is a progesterone receptor agonist and metabolite of progesterone . It is formed from progesterone by 5β-reductase. 5β-DHP inhibits spontaneous contractions in isolated rat uterus when used at a concentration of 10 µg/ml, an effect that can be blocked by the progesterone receptor antagonist RU486 but not the GABAA receptor antagonist picrotoxin . It is a negative modulator of homooligomeric Ρ1 subunit-containing GABAA receptors, inhibiting GABA-induced currents in X. laevis oocytes expressing these receptors (IC50 = 5.02 µM). Plasma levels of 5β-DHP decrease at the onset of spontaneous human labor.