Background: The glutamatergic modulator ketamine has created a blueprint for studying novel pharmaceuticals in the field. Recent studies suggest that “classic” serotonergic psychedelics (SPs) may also have antidepressant efficacy. Both ketamine and SPs appear to produce rapid, sustained antidepressant effects after a transient psychoactive period.Methods: This review summarizes areas of overlap between SP and ketamine research and considers the possibility of a common, downstream mechanism of action. The therapeutic relevance of the psychoactive state, overlapping cellular and molecular effects, and overlapping electrophysiological and neuroimaging observations are all reviewed.Results: Taken together, the evidence suggests a potentially shared mechanism wherein both ketamine and SPs may engender rapid neuroplastic effects in a glutamatergic activity-dependent manner. It is postulated that, though distinct, both ketamine and SPs appear to produce acute alterations in cortical network activity that may initially produce psychoactive effects and later produce milder, sustained changes in network efficiency associated with therapeutic response. However, despite some commonalities between the psychoactive component of these pharmacologically distinct therapies—such as engagement of the downstream glutamatergic pathway—the connection between psychoactive impact and antidepressant efficacy remains unclear and requires more rigorous research.Conclusions: Rapid-acting antidepressants currently under investigation may share some downstream pharmacological effects, suggesting that their antidepressant effects may come about via related mechanisms. Given the prototypic nature of ketamine research and recent progress in this area, this platform could be used to investigate entirely new classes of antidepressants with rapid and robust actions.

(R,S)‐Ketamine (ketamine) is a dissociative anesthetic that also possesses analgesic and antidepressant activity. Undesirable dissociative side effects and misuse potential limit expanded use of ketamine in several mental health disorders despite promising clinical activity and intensifying medical need. (2R,6R)‐Hydroxynorketamine (RR‐HNK) is a metabolite of ketamine that lacks anesthetic and dissociative activity but maintains antidepressant and analgesic activity in multiple preclinical models. To enable future assessments in selected human indications, we report the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of RR‐HNK in a Phase 1 study in healthy volunteers (NCT04711005). A six‐level single‐ascending dose (SAD) (0.1–4 mg/kg) and a two‐level multiple ascending dose (MAD) (1 and 2 mg/kg) study was performed using a 40‐minute IV administration emulating the common practice for ketamine administration for depression. Safety assessments showed RR‐HNK possessed a minimal adverse event profile and no serious adverse events at all doses examined. Evaluations of dissociation and sedation demonstrated that RR‐HNK did not possess anesthetic or dissociative characteristics in the doses examined. RR‐HNK PK parameters were measured in both the SAD and MAD studies and exhibited dose‐proportional increases in exposure. Quantitative electroencephalography (EEG) measurements collected as a PD parameter based on preclinical findings and ketamine's established effect on gamma‐power oscillations demonstrated increases of gamma power in some participants at the lower/mid‐range doses examined. Cerebrospinal fluid examination confirmed RR‐HNK exposure within the central nervous system (CNS). Collectively, these data demonstrate RR‐HNK is well tolerated with an acceptable PK profile and promising PD outcomes to support the progression into Phase 2.