For years, one of the biggest questions surrounding ketamine treatment has been why its antidepressant benefits can last long after the drug has largely cleared the bloodstream. New research examining S-ketamine brain biomarkers offers fresh evidence that the brain may continue adapting for days after treatment, providing researchers with new tools to better understand rapid-acting antidepressants.
In a randomized, double-blind, placebo-controlled crossover trial involving healthy volunteers, investigators found measurable changes in brain activity and cortical excitability that persisted for as long as seven days following intravenous S-ketamine administration. These findings may help identify objective biomarkers capable of tracking the biological processes associated with ketamine’s therapeutic effects.
Why Researchers Continue To Study Ketamine’s Lasting Effects
Conventional antidepressants often require several weeks before meaningful symptom improvement occurs, and many patients do not achieve adequate relief. Ketamine and esketamine have changed that landscape by demonstrating rapid antidepressant effects, particularly in treatment-resistant depression.
Despite this clinical success, researchers still do not fully understand which biological changes are responsible for the medication’s sustained benefits. Most previous investigations focused on the drug’s immediate effects during or shortly after administration, leaving the period beyond the first 24 hours relatively unexplored.
Finding reliable physiological biomarkers could accelerate the development of future rapid-acting antidepressants while helping clinicians better understand treatment response.
How S-ketamine Brain Biomarkers Were Measured
The investigators enrolled 16 healthy adults in a four-way crossover study that compared intravenous S-ketamine, two oral S-ketamine doses, and placebo. Participants underwent repeated assessments from baseline through seven days after dosing.
To capture brain activity from multiple perspectives, researchers combined several complementary techniques:
Transcranial magnetic stimulation with electromyography (TMS-EMG)
Transcranial magnetic stimulation with electroencephalography (TMS-EEG)
Resting-state pharmaco-electroencephalography (pEEG)
Blood sampling to compare drug concentrations with physiological changes
Together, these methods allowed investigators to distinguish between immediate drug effects and longer-lasting changes that emerged after the medication had largely cleared the body.
S-ketamine Brain Biomarkers Persisted For Seven Days
One of the study’s most notable findings was that brain activity continued changing well beyond the acute treatment window.
Immediately after intravenous treatment, researchers observed reduced motor cortex excitability along with decreases in several EEG frequency bands. These acute changes gradually shifted over time.
By 24 hours, different patterns of cortical activity emerged, and by seven days investigators detected persistent alterations in measures of intracortical inhibition and resting-state brain activity. Importantly, these delayed effects differed from the immediate pharmacological response rather than simply representing a prolonged version of the initial drug action.
The findings suggest that ketamine may trigger a sequence of biological events that continues after the drug itself has been metabolized, potentially reflecting ongoing neural adaptation rather than direct receptor blockade.
What The Brain Changes May Mean
Ketamine primarily blocks NMDA receptors, but researchers increasingly believe its antidepressant effects extend far beyond this initial mechanism.
The delayed changes observed in cortical excitability may reflect downstream processes involved in synaptic plasticity, network reorganization, and communication between brain regions. Rather than acting as a temporary chemical switch, ketamine may initiate biological pathways that continue reshaping neural circuits over several days.
The study also found concentration-response relationships for certain physiological measures, suggesting some biomarkers tracked drug exposure more consistently than others. These relationships could eventually improve how researchers evaluate future rapid-acting psychiatric medications.
Although the study was conducted in healthy volunteers rather than patients with depression, the results provide an important framework for understanding how ketamine’s biological effects unfold over time.
Why This Study Could Shape Future Research
Perhaps the most valuable contribution of this work is methodological. Instead of focusing solely on symptom improvement, the investigators identified objective neurophysiological measurements that may serve as biomarkers during future drug development.
If validated in patients with depression, these measures could help researchers determine whether experimental therapies are engaging the same biological pathways as ketamine before large clinical trials are completed.
The findings also reinforce the growing view that ketamine treatment should be understood as a process of continued brain adaptation rather than a brief pharmacological event.
As precision psychiatry advances, combining TMS, EEG, and pharmacodynamic biomarkers may improve both treatment development and the ability to personalize care for individual patients.
While additional research in clinical populations remains necessary, this study provides compelling evidence that measurable brain changes continue long after ketamine administration, offering new clues into one of psychiatry’s most promising rapid-acting treatments.
Citations
de Cuba CMKE, et al. Sustained pharmacodynamic effects of S-ketamine on cortical excitability and resting-state brain activity: A randomized, placebo-controlled trial. British Journal of Clinical Pharmacology. 2026. https://doi.org/10.1002/bcp.70649
PubMed. Sustained pharmacodynamic effects of S-ketamine on cortical excitability and resting-state brain activity: A randomized, placebo-controlled trial. https://pubmed.ncbi.nlm.nih.gov/40669764/