Exploring the Therapeutic Potential of Psilocybin and Ketamine in Major Depressive Disorder including Treatment-Resistant Depression: A Narrative Review

Major depressive disorder and treatment-resistant depression are global health challenges where conventional therapies often fall short. This review examines psilocybin and ketamine, two agents with distinct mechanisms from traditional antidepressants. Psilocybin, a 5-HT2A receptor agonist, shows rapid and sustained antidepressant effects, with clinical trials reporting response rates of 54-71% in MDD. Ketamine, an NMDA receptor antagonist, acts via glutamatergic pathways and reduces suicidal ideation within hours. Psilocybin requires structured psychotherapeutic support during its acute effects, while ketamine offers flexible administration routes, some usable in emergencies. Both have favorable safety in controlled settings, with transient adverse effects like dissociation or nausea. Current research is limited by small samples, blinding challenges, and trial heterogeneity. Large-scale trials and standardized protocols are needed for clinical integration.

Study at a glance

Abstract

Abstract Major depressive disorder (MDD), including treatment-resistant depression (TRD), represents significant global health challenges with conventional therapies often yielding suboptimal outcomes. This narrative review examines the therapeutic potential of psilocybin and ketamine, two novel agents offering distinct mechanisms of action compared to traditional monoamine-based or monoamine reuptake inhibitor antidepressants. Psilocybin, a 5-HT2A receptor agonist, induces rapid and sustained antidepressant effects with some clinical trials demonstrating response rates of 54-71% in MDD. Ketamine, an NMDA receptor antagonist, exerts rapid antidepressant effects via glutamatergic signalling pathways, showing particular efficacy in reducing suicidal ideation within hours. While psilocybin requires structured psychotherapeutic support during its acute psychedelic effects, ketamine offers flexible administration routes (intranasal, intravenous, subcutaneous), some of which can be applied immediately in an emergency setting. Safety profiles for both compounds are favourable in controlled settings with transient adverse effects such as dissociation or nausea. However, current research faces limitations including small sample sizes, blinding challenges, and heterogeneity in trial design and therapeutic protocols. Despite these constraints, psilocybin and ketamine represent a paradigm shift in depression treatment. Future directions require large-scale trials, standardized protocols and long-term safety assessments to optimize their integration into clinical practice. These agents hold promise for reshaping therapeutic approaches to MDD, particularly for patients unresponsive to conventional therapies (TRD).