The relationship between stress hormones and mood disorders is more nuanced than the popular narrative suggests — and a new finding from a controlled ketamine trial adds a surprising twist. Rather than functioning purely as a stress marker to be suppressed, cortisol may actually play a constructive role in how certain rapid-acting antidepressants produce their effect, at least in the acute phase following treatment.
In this exploratory analysis nested within a midazolam-controlled randomized trial of intravenous subanesthetic ketamine for suicidal depression, researchers measured the cortisol awakening response — saliva samples taken at waking and 30 minutes later — at baseline and again 24 hours post-infusion. Among 62 participants, waking cortisol levels rose significantly the morning after ketamine infusion (t(61) = −3.15, p = 0.0025). A trend-level correlation (r = −0.25, p = 0.052) suggested that larger cortisol increases were modestly associated with greater reductions in suicidal ideation, though this relationship did not reach statistical significance.
This finding challenges the reflexive assumption that cortisol elevation always signals harmful stress dysregulation. The broader neuroendocrinology literature has increasingly distinguished between pathological hypercortisolism — chronic, blunted, or flat awakening responses — and transient, appropriately calibrated cortisol surges that appear to support neuroplasticity, fear extinction, and stress resilience. Ketamine's known mechanism involves rapid glutamatergic modulation and BDNF release; whether cortisol elevation is a downstream biomarker of that cascade or an independent contributor to clinical response remains unresolved. This is an exploratory, single-timepoint analysis with a modest sample, so causal claims are premature. Replication with larger cohorts, longer follow-up cortisol tracking, and HPA axis profiling at multiple post-infusion windows would substantially strengthen the inference. Still, for researchers mapping ketamine's biological footprint, the HPA axis now warrants more deliberate attention.