The Hypothalamic-pituitary-adrenal (HPA) axis plays an important role in the pathophysiology of mood disorders, and preliminary data suggests that glucocorticoid receptor (GR) antagonism may be an important therapeutic mechanism. The effects of modulating HPA axis function on emotional processing related brain activity, which may be abnormal in depressed mood, is poorly understood. This study used a pharmacological functional magnetic resonance imaging (fMRI) design to determine the effects of the GR and progesterone receptor antagonist mifepristone on emotional faces processing task related brain activations in 19 right-handed healthy male participants. Each participant received 600 mg mifepristone or placebo on two separate imaging days and then performed an emotional processing fMRI task four hours later. The effect of mifepristone on task related brain activations was determined using Region-of-Interest (ROI) analyses and an exploratory whole brain voxel-wise analyses. No significant changes were observed in the defined ROIs (amygdala, anterior cingulate cortex, insula) or in the exploratory whole brain analyses that was associated with mifepristone administration in either the angry vs happy faces or angry and happy faces vs implicit baseline contrasts. Task reaction times and accuracy were similar in both mifepristone and placebo conditions (all p > 0.05). Our study failed to show significant evidence of modulation of emotional processing related brain activity associated with acute mifepristone administration. Future research should use fMRI to investigate the longer-term administration effects of mifepristone on mood in healthy participants and people with mood disorders to provide a deeper understanding of the potential effects on depressive symptoms., Competing Interests: Conflict of interest Nefize Yalin has worked as a researcher in clinical studies conducted together with Jannsen Cliag, Corcept Therapeutics, COMPASS Pathways, H. Lundbeck A/S and Sosei Heptares and Neurocentrx in the last five years. Allan Young is the editor of Journal of Psychopharmacology and Deputy Editor for BJPsych Open. He has conducted paid lectures and advisory boards for AstraZeneca, Boehringer Ingelheim, Eli Lilly, Lundbeck, Sunovion, Servier, Livanova, Janssen, Allegan, Bionomics, Sumitomo Dainippon Pharma, COMPASS, Sage and Novartis and Nuerocentrx. He is the Principal Investigator in the Restore-Life VNS registry study funded by LivaNova, ESKETINTRD3004: "An Open-label, Long-term, Safety and Efficacy Study of Intranasal Esketamine in Treatment-resistant Depression", "The Effects of Psilocybin on Cognitive Function in Healthy Participants" and "The Safety and Efficacy of Psilocybin in Participants with Treatment-Resistant Depression (P-TRD)". He is UK chief Investigator for Compass COMP006 & COMP007 studies, Novartis MDD study MIJ821A12201. He has received grant funding (past and present) from: NIMH (USA); CIHR (Canada); NARSAD (USA); Stanley Medical Research Institute (USA); MRC (UK); Wellcome Trust (UK); Royal College of Physicians (Edin); BMA (UK); UBC-VGH Foundation (Canada); WEDC (Canada); CCS Depression Research Fund (Canada); MSFHR (Canada); NIHR (UK). Janssen (UK), EU Horizon 2020. He has no shareholdings in pharmaceutical companies. Matthew Kempton and Ndaba Mazibuko have nothing to declare. Mitul Mehta has conducted paid advisory work for Neurocrine, Neurocentrx and Lundbeck. He has received research funding from Lundbeck, SoseiHeptares, Neurocentrx and Takeda. Paul Stokes reports grants and non-financial support from Corcept Therapeutics during the conduct of the study. He also reports non-financial support from Janssen Research and Development LLC, personal fees and non-financial support from Frontiers in Psychiatry, personal fees from Allergan, and a grant from H Lundbeck outside the submitted work., (Copyright © 2023 Elsevier B.V. and ECNP. All rights reserved.)